Not that unusual, from what I've seen. Just typical head-scratching donkey play. But I'm not sure what you're mystified about.
I don't know any of the history between these two players or how they've played in these positions. This could be a case of superb, incredible reads or two donks donking.
CO (jack)
Tries to steal from limper/blinds
Loves his big paint vs. all little cards on the flop
He c-bets
Then fires another big shot -- that would usually get a bad hand to fold
MP (xxG)
Has Ax and limps
Then "defends" his limp cause he loves any Ace.
Calls the flop c-bet cause he thinks he might be ahead (he's right) and/or he still loves his Ace
Calls the All-in on the turn because he's incredibly smart or incredibly stupid. In fact he's ahead, but most players would lay it down here unless he thinks the other guy is really full of it.
Paired up on the river, though he didn't even need it.
Won the hand by sheer stubbornness, stupidity, skill, or luck -- take your pick!
I see lots of play like this in heads-up matches, though that's a little different.