Your analysis on the flop is okay to a point, but...
It's not highly likely but also not impossible for him to have a 5. With his stack, he can certainly afford to speculate. So he could, for example, have decided to call in position with something like A5s, suited connectors, maybe even suited gappers. Or 55.
He also has ample implied odds
to set mine with 22.
And engrave what Mediablitz brought up into your poker consciousness. Do not assume other people play like you. Or that they play the way you'd like them to because it would be comfortable for you.