bad fold?

[lingdog]

hi everyone
i played a MTT at my local casino the other day, the guy to my right was a pretty decent player, the rest of the table are not so good.the blind is 100/200, my stack is around i picked up KJ offsuit in the big blind, 4 limpers, small blind just called, and i checked. the flop came J 8 4 rainbow, small blind checked, i bet 700 hundred into a 1200 pot. every1 fold excepts the small blind called, turn card is another 4. small blind bet 1000 into 2600 pot, i called (may be i shouldn't of). river card is
and Ace. he bet 2000 into 4600 pot, i have 4000 chips left and i folded.
what can he possibly have?
was he on a draw? 9 T, 5 6? so bluffing on the river
a set may be? 88? would he of checked raised me on the flop?
another 4 giving him 3 of a kind?
or a jack?
so is it a bad fold?
any feedback will be much appreciated