How much and how many?

A forwarded message in my inbox, with the subject line: ‘Dr Faustus says: Someone doesn’t realise that you can count people...’ Here (edited slightly) is the offending email:

Dr Faustus commented: ‘Fewer than 18 students! Fewer than! /rage.’*

* The OxfordDictionaries page ‘“Less” or “fewer”?’ explains how to tell when to use less and when to use fewer. I’d also point out that the correct UK-English spelling is enrolment, and the use of the hyphen (presumably meant to represent a dash) is erroneous, since the ‘Many thanks’ clause and the passage beginning ‘unfortunately’ do not share a subject and should be separate sentences.