Well, from his reaction to seeing Ben, it seems pretty clear Ben had not appeared to him before so Ben would not have been teaching him from beyond the grave. Otherwise there would be no need for Yoda.
It would not make sense for Luke to simply give up on the Force for the three years between ANH and TESB. You wouldn’t go “oh well, my mentor’s dead so I’m out”. The implication is that he kept training - to whatever extent. “But I’ve learned so much” is an indication of that.
The Marvel series had Luke training with remotes, meditating, using the Force in battle, and communing with ghost-Obi Wan. This obviously doesn’t count as ‘canon’, but it does indicate the logic of assuming Luke would carry on as best he could. Marvel were on a tight leash with regard to how much they could develop these characters, and they did not know the details of TESB until very close to the movie. There was a fan letter in one issue circa mid-1980 that said something like “you need to pick up the pace because it looks like Luke will be levitating small objects in the next movie - you guys still have him practising with his Lightsaber”. Again, this is a fan assuming the logic of Luke self-training as best he could. Yoda never said “download these skills you must, save time you will”. Training is crucial in the OT. Not in the ST.
one thing about that original Marvel series you did not mention is that in issue 23 , Luke was able to reach out telepathically and touch Vader’s mind , eliciting a very loud scream of agony from Vader . Pretty advanced stuff for a fledgling Jedi ! No one taught him that trick , but hey , it’s not “canon” after all…