Yes British Muslims, on average, have more regressive attitudes towards homosexuality than the rest of the UK population, though how far private beliefs lead to public action is another matter.
In highlighting Muslims, the implication is that there is something distinctive about this group, that it provides additional information about attitudes. In principle, homophobia might be found among the wider British public of which Muslims are a subset. Ockham’s Razor reminds us that among competing explanations, we should always choose the simpler, more general explanation.
As such, you correctly use a baseline to show that attitudes among Muslims are, in practice, different from the British public. Of course, the British public is not the only group to which Muslims belong: they are also a religion, among other things. Just in the same way you use a baseline to differentiate Muslims from the British public, it also makes sense to compare Muslims with other religious groups before drilling down further and using more detailed ascriptions or categories to understand the issue.
Thus, Jonnyboy is quite correct to ask whether homophobic attitudes are shared among other religious groups. It is not whataboutery or irrelevant deflection: it’s simply good science and logical reasoning. HTH.