In a nutshell, your armchair speculations are meaningless unless you have scientific credentials and studies to compare with those being reported.I think that is a stretch.
An analogy for singularly lingual people might be switching from speaking a language, to singing in that same language. While the vocal activity is similar, the actual level of focus in no different than speaking another language. In other words, if you can switch from speaking to singing, then you have the same "skills" as someone that is bilingual, in a nutshell.
And many low level ones who speak many languages. Misleading anecdotes are easy to come by.As related to Pool, there are a bunch of very high level poolplayers, foreign and domestic, that only speak one language.
pj
chgo