Gaffer Tape said:

Oh, I think I figured out how R2 got in there. What ady didn't show us is the preceding footage where there's actually a hole above the cave. In the last shot, R2 flies up in the air with his rocket boots, does a little figure 8 and a somersault and then lands deftly in the cave. I mean, obviously it's to match the prequels. It's like poetry.

Blast, I was all set to go with this same joke.

Have they done as I suggested and removed the X-Wing from Dagobah? When Luke has to go save Han, he just fixes a bicycle seat to R2's dome and together they set off for Bespin.