I think you've hit the nail on the head. I see this phenomenon a lot with baseball fans of advanced metrics. The general idea behind these advanced metrics is that you get a better chance of predicting a player's most likely outcome, but people look at these stats to show that definitely outcome X will happen because "Look at these overwhelming numbers I have on my side", as if nothing can ever change. Well, of course things can change. Players get their eyes checked, players get injured/healthy, players change their swings, pitchers change how they approach hitters, players become more mature, etc. The thing is, I don't need to provide you with an explanation as to why numbers can change from the minors to the majors (or within the majors) because it happens. You'd think Blue Jays fans, who just witnessed what Bautista and Encarnacion did, would realize this. I'm not saying this happens often, that's why advanced metrics work, but it certainly does happen.
Now, if all tercet was saying was "Look, maybe Teoscar has changed but his numbers from his career show this is likely not sustainable so I'd rather bet on those numbers than whatever purported change you claim" I may agree with him. I think people can very easily create post-hoc explanations for players on a hot streak (e.g. Goins and his bat resting on his shoulder) that are really not the true explanation. But his complete trust in the numbers without ever contemplating that he doesn't have every single variable accounted for to 100% accuracy is absurd. It is as if he truly believes that if you just gave him the data and a computer that he would be able to build a World Series winner every year without doing anything other than seeing who has the best WAR and K rate etc. historically.