Or there could have been further incidents outright establishing that Romulans are renegade Vulcans. But that's not necessary, merely a plausible addition, if we go the "Comms Lieutenant doesn't know Polish from Russian" route. It just differentiates between two outcomes if Pike actually contacts the Romulan Star Empire over Nero's antics: Romulans grunt that they have nothing to do with this Nero character and close the channel, or
Romulans go to utter panic because the Federation has somehow found out they are pointy-eared, green-blooded ex-Vulcans!
But there's another aspect to this:
Except they were speaking one of the known dialects of Romulan.
On the background, yes (although Ayel might have been speaking English). But how does the UT actually work? After the translation is done, is it possible to learn what the original language had been?
Most probably there would be ways to dig up the information after the fact, by opening a "toolkit" menu and rummaging through the short-term memory of the device. But the device died with Robau... Would a putative transmission from Robau to Kelvin
have carried this "comment track" or just the translation?
Then again, Sisko has to learn to speak Bajoran to conduct ceremonies. Yet most Bajorans can communicate with Sisko all right, before
Sisko learns any Bajoran - and Bajorans don't strike me as the type to stoop to learning foreign languages. If Bajorans have UTs that turn Sisko's English (French? Creole? Personal mumbling?) into Bajoran, how can they tell whether Sisko is conducting a ceremony in Bajoran? If we assume they can (and it's not something Sisko does simply because he finds it spiritually necessary), then the UT most probably could also reveal the original language of Ayel, down to nuances such as dialect. And the UT could do that fairly trivially, not just with expert help. So if the Kelvin
crew eavesdropped, they might have gotten some clues, too.