The issue is really focused on the grammatical function of the word. The researcher is arguing that it's not ever used as an interjection, which "whoa" always is.
I would say the presence of an exclamation mark, in a context where exclamation marks are rare, is strong evidence of use as an interjection. Unless we're arguing that some other mark was mistaken for an exclamation, generally I would say rare typography is "marked" (noteworthy) rather than being likely mistaken. I think the researcher's position is not likely to hold much sway going forward.
I would say the presence of an exclamation mark, in a context where exclamation marks are rare, is strong evidence of use as an interjection. Unless we're arguing that some other mark was mistaken for an exclamation, generally I would say rare typography is "marked" (noteworthy) rather than being likely mistaken. I think the researcher's position is not likely to hold much sway going forward.