I believe it to be a single case, seen from two sides:
- simple side, often as seen on a news reel, or description sent to loved ones ("car bomb")
- from those that were there ("hotel came down on us")
From a transcript:
You got fat, Dave.
I was in the same lobby...
...when that bomb went off.
Looking right at you...
...when that hotel came down on us.
You were there and then you weren't.
Wasn't my day.
So, in the first film, I wrote it off as a simple car bomb, nothing more to be said.
When they expanded upon it in the second film (and there is nothing to say that the core of the idea was not there in the first place in the first film, it is the same writer after all), I really did not query it, as it immediately brought to my mind so many situations when that could have occurred in that way, and one of those ways, was the following:
It reminded me of a particularly well-known (or infamous) incident that occurred in real life (one of many similar, obviously - see PoloHoleSet's comment on Mount Lebanon hotel car bomb back in 2004) but it would have been a combination of bomb/hotel/lobby/size/US-personnel-as-targets/recent-memory for the writers that places this incident as likely inspiration (for want of a better word), at the top of my mind:
This was a truck bomb, detonated before it could enter the Marriott Hotel building lobby itself, but even so, it was so large it made a devastating impact regardless.
- in official channels, on the news etc, it would be a truck bomb.
- to those that were there, in the rubble, in the before and the immediate after, especially for those in the immediate vicinity, it would be a bomb going off bringing the lobby down on them.
So, the following could be true if it were the case that the back story for the car bomb was already thought about when developing the first film:
The bombing was big news in 2008, the film was in development from at least 2010, and in the writing or treatment process well before this, Denzel was announced as lead in 2011, shooting (ahem) began in 2013.
Also, as much as I would rather refrain from connecting the dots with real life, the reports following the blast cited various targets or reasons for the attack, such as: 30 US Marines staying at the hotel, US 'Security Agency' personnel staying at the hotel (might be the same groups listed here), several senior CIA personnel were allegedly staying at the hotel; later, a US State Department employee was listed as missing, presumed dead. NSA later listed one of their own as a casualty.
So a high profile 2008 vehicle bomb resulting in the devastation of a hotel lobby (and deaths), involving US personnel presence that may or not involve particularly sensitive agencies (ie. CIA), is highly likely to have been within earshot of the writers at the time.
I am not sure of the people involved nor timeline of the story development but anyone involved in that region (including over the borders) by whatever means, whatever agency, private and otherwise, during that period of time, would be very familiar with the security situation and the incidents such as this that occurred.
Note that the sequel was announced with Wenk penning, as he did the first, in February 2014, seven months before the first film was released, so it would not be unlikely that he could have continued or expanded upon the original idea, inspired by real world events.
Going back to the story, if McCall was already on the way out, and that incident happened to be the situation at the time, then it seems to be a case of situation provides the opportunity. As in real world cases, identification can sometimes be difficult, and if enough clues are placed then assumptions will be made.
Nothing to say that McCall made the bomb happen, just that it was the time that everyone noted that he simply was no longer with them.
Car bombs are just that, bombs in vehicles, doesn't mean to say that the side effects of that bomb detonating are limited to that car.
I found an interview (2015) that sort of supports my theory about Wenk (writer) and potentially placing his research period around the time of the Marriott Hotel bombing (and subsequent reports of what type of American presence was there):
as I mulled the idea to do it, I dug out an article from the Wall Street Journal about a poll listing five things for Americans in 2007-2008 to make their life better – the top thing was justice
I’m toying around with “Equalizer 2” – depending on how it’s received, I thought the story would continue anyway
The original idea was about a man who, as a former cover operations officer, tries to make up for past sins by helping people who are in trouble.
He did some bad things that not many people had done, he has some skills.
WSJ, bombing article: https://www.wsj.com/articles/SB122194909512860313