It IS an odd thing to say. Unless one is really bad at math. As usual Rafans and Nolefam counting their chickens before they hatch. You haven't learned from the past at all.
How is it odd? People were calling Federer GOAT when he was like 5 slams behind Sampras, on the presumption that he was defintely going to get past 14 slams. Federer fans were not complaining about maths then. But to be fair, people were right. It was inevitable, and Federer did pass Sampras total comfortably
I actually think it's a lot more reasonable and respectful for people to call Nadal GOAT (if they are inclined) with ONLY a 1 slam deficit. I (and many others) think it's inevitable that Nadal cruises past 20. Nadal is about to become the world no.1 again. I'd say winning two more slams is more likely than not.