I don't see any problem with it either, my understanding was that the following weight classes existed around (and slightly before) that time:

Mainframes = room sized montrosities

Minicomputers = multi-cupboard units

Superminicomputers = just one cupboard or small fridge

Microcomputers or personal computers = these guys in the article

I don't see an issue either. Micros aren't just C64s and Spectrums. It's everything below a mini. An early IBM PC was a shadow of the class dominating supercomputers they are today.