Whilst fighting to remove some old bearings from my norco I have take apart the bike and found a tiny hole where the disc brake screws into the frame . It looks to me like its where’s the bolt itself goes in.

What do you think? Fatal? Ok and normal?

Too long a bolt has been fitted at some point. Done the same to a set of forks i didnt die.

I’d say you’d bottomed a bolt out in the thread part of the mount and broken through.

I’d not worry but make sure you grease the bolt so it doesn’t sieze.