Bananas can develop black spots as they grow but wipe him down with a damp paper towel and inspect his eyes and heatpits.
You are looking for little black dots about the size of this period.
If it is mites then you will need to treat all your snakes/ enclosures as you completely skipped quarantine.
ETA: missed the bit you mentioned the black spots - I should stop speed reading at this time of the morning.