This shouldn't be surprising. You pretty much need formal training in mathematics of some sort to be able aspire to even be an amateur mathematician. There are many people with math degrees out there, it's just that most didn't pursue careers in mathematics.

An amateur is not a person that has no knowledge.

An amateur is a person who pursues an activity independently of their source of income.

It's kind of amusing that general understanding of the term has flipped in this way - basically it implies that if you're not doing something under a capitalistic structure, you're probably doing something wrong.

A bunch of software that you use on your computer on an everyday basis was produced by amateurs.

Hobbyist might be a better term.

I have a degree in Physics. I'm not even an amateur physicist - I don't really do anything in the field at all, my time is spent moving pixels about on screens. :P

In the sense that this person does not do maths as their full time job. Most folks writing papers and finding new proofs, etc, do.

This is nothing extraordinary, there are many people having a math Bachelor or Master. Also a famous university name on your BA/MA tells nothing about your level. University get their ranking through research publications not through undergrad math test . So what really matters is whereas you choose to dedicate (a part of) your life to Math or not, there is no secret magical course at Cambridge that will enlight you, courses are pretty much the same in all big universities

Most people who get maths degrees from Oxbridge don't go on to be professional mathematics though. Out of the 7 I know only one did. The others basically don't do complex maths anymore.

An undergrad degree; his PhD was in a different field. So yes I'd call that "amateur".