I suspect your friend is confusing GB with that other country called Europe*.

It is "point" as in "one point five" here. We always use the "decimal point" (period character) to separate wholes from fractions, never a comma. A comma doesn't make any sense, except as a thousands separator.

As far as expressing fractions goes, my experience is that that is down to age and arithmetic awareness. Specifically; we measure distance here more in millimeters than we do inches (but we measure long distances while driving in miles!). People more accustomed to dealing with inches tend to be more used to fractions; 1/8th, 3/16th etc. Similarly, those people will recognise values like 0.25, 0.5, 0.75 and express them as "quarter", "half" and "three quarters".

* - While working for a number of American owned multi-national companies I realised that some Americans thought Europe was a country. Taking this into account, it's not difficult to imagine how some Americans might mistakenly think that the 'European' use of "comma" as a whole/decimal separator would also apply to the UK. Incidentally, and anecdotally, I couldn't actually tell you what European countries use comma as a decimal point!