It could be so many things.

Could be a
-faulty oil pressure gauge
-knackered oil pump
-blocked oil feeds
-blocked strainer
-worn mains
-worn big ends
-worn cam journals

and a few other items.

You can whip the big end bearings off easily enough without dropping the engine if you wanna take a gander. Equally swapping the pump can be done in situ (bit fiddly but not that bad) if you want to take a chance, but if its been running at genuinely 10psi cold, then damage will definitely have been done. A couple of degrees and that oil/engine must have been running at as good as 0psi