I don’t think the bb will go all in with a pair of Ks or Js especially when you led into him after the flop. He could have A3 or A5 suited and raised pre-flop as a squeeze. Either way, you were dominated there. I totally understand why you call: top pair very good kicker (i probably would have done the same). But all you beat is Aj which would have just called your bet instead of going all-in. my 2 cents.