There are two possible answers to this question. Either he didn't think too much of it, or he was setting aside money for Sean.
The closest answer we can get from Han himself is Han's comment about it when DK confronted about it: "We ain't the boy scouts. This is what we do". He was dismissive of DK's concerns because he didn't seem to think of it as all that big of a deal, especially since it's probably not a lot of money. The assumption that it really isn't a lot of money is further reinforced by the scene DK's uncle pointed it out, DK told his uncle that it probably not a lot and and the uncle, rather than contradict him, equates that sum of money as a nail in his proverb. This is even further reinforced that that money was in a duffel bag, just sitting in Twinkie's car, in full sum. There is good reason to believe this is Han's money because when Twinkie handed it over "Han probably would have wanted [Sean] to have [this money]". This heavily implies that Han had a say where that money went, because it was his money.
This brings us to the other possible reason: It was for Sean. The straightforward reason for setting aside that money would be that it was an emergency fund set aside for Sean, as in "Han probably would have wanted you to have this money if something bad happens". The other possible reason is that Han meant to give it to him once Sean had finished "paying" him back for the car he broke. This way, it would clear out all the possible bad taste Sean would have had for being tricked into working for him, but only after Han was happy enough with the amount of mentoring he has doled out on Sean.
As for Han's financial status, it has been 1-2 years after fast 6, and several years after the heist that made him rich. We do not know what Han was up in that time period and how much money he was spending.
It is also important to note that while Tokyo drift takes place after fast 6, it was released as the third in the franchise and have changed Tokyo Drift's continuity (i.e. changing the year it took place) and while he may have been rich in Tokyo drift, the exact amount of his fortune was retroactively defined in Fast Five and that fortune size may not truly reflect what Han was implied to have in Tokyo Drift.