If UTG+1 is pretty straightforward and rock-like hes pretty unlikely to limp/coldcall anything preflop that even connects with that board (except maaaaaybe TT which he cant have here anyway). Id guess he has something like 88 and thinks he needs 8:1 to sethunt.
MP1s range is so wide he can have any of the 2pairs or pair + straight draws aswell as weak Ax and hes stacking with a lot of his range. IF UTG does go mental then the chance he played some random crap that flopped 2 pair in a weird and wacky way has to be at least as big as the chance he played AA in a weird and wacky way.