Those terms come from the 70's when PC meant 6502, 6800, 6809, Z80 or other 8 (and later 16) bit small computer which was meant for a single user instead of the time sharing minis and mainframes.

No wonder newer generations who missed the transition from minis and mainframes to personal computers find it very confusing.

Your honour, I present exhibit 1:

http://codytaylor.org/images/apple/apple-computers-personal-...