No, whatever would give you that idea? it's pretty clear in the context of what he said overall that he meant "back (in time) in December," but your post suggests that the word back can't be used this way, which it definitely can.
Imagine rolling with Parker Porter…
Man, it's so tempting to change one of his names to "porker" but both first and last are like equally close. Porker Porter? Parker Porker? Porker Porker?
Isn't it obvious that he said that "Back in December, he got his black belt", rather than "In December he got his black belt back" ?
Parker Porter > Khabib...well, yes, but what else are we gonna talk about?
Khabib simply can't be in the GOAT discussion with so few top 5 wins.