I would guess, from everything I've seen about Young and the FSU, because it is.
> Are they just normal libertarians?
Well, right-libertarians are a common subset of normal libertarians (in the US, most—but not remotely all—who identify as libertarians are right-libertarians, non-right libertarians are more likely to identify differently, but I don't think that that soft tendency applies to the UK, at least in the same degree.) So, sure in one sense they are “normal libertarians” but not representative of the broader group, AFAICT.
> The vast majority of libertarians do not self-identify as being 'right-wing'.
So? The FSU is not the vast majority of libertarians, and descriptions of someone's policy position can be independent of their self-identification.
A Nazi doesn't become a moderate just because they self identify as “moderate”.