That's what one would imagine any "proto-" prefix should indicate, yes. However in this case the claim is that the "proto-" version was in use centuries after Romance languages had long become vernacular, and the justification for this claim is what the researcher has described as "lateral thinking" on his part in guessing that the "proto-" version of romance languages had been retained as a sort of private code used in nunneries. None of this, at least has yet, has even the slightest historical justification and the researcher's plea that his "findings" should be accepted as "blind peer-review" has yet to gainsay him simply shows that he either fails to understand how peer-review works, or hopes that the general public certainly don't!
Always distrust historical "findings" that make it into the press before the review process has at least provided a second paper backing them up. If one takes it as a rule of thumb that such cases reveal a researcher trying to make a name for himself rather than anything new in the actual research sense, then one is rarely wrong.