motherboard labeled as incorrect

I would imagine the fm2a85x label is a sticker as the 2 boards are completely
different in layout (one being mATX and the other standard ATX).
My guess would be that someone purchased 2 boards, the more expensive fm2a85x extreme4
and the fm2a75 Pro4 then pulled the sticker off the more expensive board and put
it on the cheaper one then returned the cheaper one in the more expensive one's
box.
I have seen things like this happen all too often over the years. Then once the
board was tested by the store/outlet and found to be good it would have been
put back into inventory.

That is pretty common then That means it came from the factory like that.
If you look at both the boards:

https://www.asrock.com/mb/AMD/FM2A85X%20Extreme4-M/index.asp
https://www.asrock.com/mb/amd/fm2a75%20pro4-m/

They use the exact same PCB layout. At some point they must have run out of the
PCBs for the a75 variant and had an excess of the a85 ones so just put a sticker
over the silkscreen that reads a75. The components on the PCB will be that of the
a75, it's just the silkscreen that's wrong.

I have a few boards like this, if you remove the sticker it has a different
silkscreen underneath. It's common practice to avoid e-waste.