[rflrob]

I think it's unreasonable to expect the namers of a language to know every conceivable double entendre in every language. Coq was named by French researchers, and means "rooster", and pqR is obviously from the sequence of letters. Neither of those seems particularly immature to me, in context.

[extra88]

Yes, it's the sequence of letters but that's not all. From the first line in TFA, "pqR — a “pretty quick” version of R."