In looking at my old reference database (~300,000 good quality and relatively contemporary games at/before 2020) R+B v R with pawns on either side showed up 5.6

In looking at my old reference database (~300,000 good quality and relatively contemporary games at/before 2020) R+B v R with pawns on either side showed up 5.6% of the time. The exact ending with 0 pawns showed up 0.15% of the time. That's probably understating it since it's more likely to occur against relatively evenly matched players. It's also going to depend on the style of the players. Caruana, for instance, had it at least 10 times including 4 wins (starting from theoretically drawn positions) against 2666 rated Guseinov, 2765 rated Radjabov, 2557 rated Gareyev, and even one kind of against 2809 rated Aronian. The one against Aronian needs an asterisk because they were playing with both sides having 1 pawn (in a still theoretically drawn position) and eventually Aronian voluntarily transposed into a completely lost RB v R ending. So 1.6% is very much in the realm of possibility depending on the specifics of the dataset. 1 in 5000 is difficult to imagine by any composition. It might have been a typo in his notes and he meant 1 in 500? That probably is underestimating it, but it's at least an order of magnitude closer to the right ballpark.