So I had my favorite seat booked, but upon check in I was notified that the seat that I was picked had a broken IFE and I was proactively moved to a different seat. Okay, thanks I guess?

Well to my surprise when I board I find someone else in that seat? So what are they going to offer compensation to that passenger (though apparently an op-up)? Because I didn't even use the IFE during the whole flight, so I would have liked my original seat. The original seat was a bassinet seating, but the passenger in the seat did not have an infant.

I am more confused and just wondering if I was kicked from the seat for some other reason or someone misrepresent their situation to get the seat I picked well ahead.