I don't think these two guys were made because made guys don't do that kind of collections with such small money.
Anyway, just like Walt and freeling10 said in the comment section, I think at the moment he was surprised as he invented a stupid excuse "It's a joke!".
Also he doesn't have his gun on him at this moment, so he couldn't instantly follow them and kill them in the parking lot for example. Just after this scene, at 42:58 on the episode, he goes home and take his gun in his bedside table then we can see him taking cash, then leaving on the run.
Another thing I thought, is these two guys are from Lupertazzi family (New York) and Vito is from New Jersey so he might know them, but he probably doesn't know where they live so he couldn't be able to track them home before the rumour spreads.
The knowledge of his bisexuality would spread so fast that he decided to flee instead.