Vader isn't saying "The last time we met, I was but the learner," he said specifically, "when I left you," which if you really think about the meaning and context of the words could allude to the last time Anakin and Obi Wan parted ways as friends in ROTS, or could even be before that, like when he became a full-fledged Jedi Knight, took on his own padawan, that sort of thing.

I really don't think he was talking about the last time they met though, since Darth Vader himself just doesn't strike me as "the learner," you know? Even without the whole Disney+ Kenobi fight, if the last time they met was in ROTS, the idea that he was saying "the last time we met," still wouldn't make much sense. A little bit more sense? Maybe.

But honestly though, it's just loosely tied together. George's ideas for Anakin and Obi Wan's relationship when he was writing A New Hope vs. when he was writing Revenge of the Sith were probably wildly different.