May you please explain: Strange play at $530 on party

[tozzy]

Hell, I'm not playing those, I just observe them from time to time for educational purposes. However, following hand did just happen:
Blinds 100/200
MP1 @ ~1600 raises to t1000
MP2 @ 600 calls All in
CO @ ~5k pushes , MP1 calls.

MP1 flips over A9o, Mp2 shows KQo and CO shows QJs.
I dont play this limits and dont plan to do so for a long time, and so I'm sure there is some higher level thinking involved, aswell as reads ofc, but I just don't get MP1's move.
Does he believe to feint strength with doing this awkward raise, why then obv. commiting himself in such a strange way?
And what is CO's intention? Is he just getting propper odds for the both of them (likely to be dominated), is he overthinking MP1 (i know he knows that i know stuff) and believes his hand to be good?
Enlighten me please.

[Paul B.]

omg I need to get back on party