I think the point is that 0.5 is 1/2, and the 5 digit only appears because of our base 10 presentation of numbers.

I think the context was perhaps more important than I'd considered to explain the significance of "five-y". The implication was that the fiviness gives something of an intuitive explaination for why some shape had 5 sides. The presence of a √5 does (maybe) do this, but 0.5 definitely doesn't. (Because as sibling comment points out, 0.5 = 1/2 and the 5 only appears due to our (arbitrary, from a mathematical point of view) choice of base ten.