I believe he probably had the flush. It is an awful attempt at gaining value from a big hand when you played way too weak to build the pot the right way.
Poor play, probably a poor player (think long-term EV from making moves like this...) --> Anyways it makes sense why the pot was so small if he was on a draw. Easy fold over small pot.
I think another part of the problem is the lack of interaction at a cash table online. You have no idea who you are sitting with, its just two cards on a monitor. It could be Bill Gates over there or just some young schmuck like me without a lot of money to burn. It is nice when you know what kind of level the person is playing at mentally. If the guy tips $17 every time he gets a pizza or a cab ride he probably doesn't think much about shipping it off to you as part of some outrageous fun online. There are people like that who gamble just for the game of it not to make any living but just to punk people in hands and feel like a pro.
Personally I have been going with the strategy in our live cash games of making tricky value bets on the river when I am bluffing
. I try to make it seem like I want a call when I really don't, choosing a bet size that is within their calling range throughout the hand. If I find the right threshold people will fold especially if I have the lead. Sometimes I get called by a schmedium strength hand, then I know I should have bet a little more...but over time I think this will limit my losses due to bluffing and make me harder to read as an unpredictable opponent. FYI my overbets are about 50/50 but never 4x the pot. Why bet 4x the pot when 2x gets the same job done?! That guys a fool