[spivey]

He could have flopped a set, and is checking river to let you bluff missed draws, rep something worse than a K so you'd vb with it (your hand is pretty well polarized to a K or a draw), and then he's shoving over your river bet for value obv.

Only odd thing is turn bet sizing, which seems small for a set, but he could have been trying to induce, or he may just bet kind of funky.