These do look like galls, yes, and they are probably mite galls, which can be common on a variety of different tree and shrub species. The linked page illustrates some examples. Despite being a bit of an eyesore, they are not harmful to the plant over the long term, and can be ignored. (If too bothersome, the worst of them can be trimmed off, if doing so won't remove too much of the plant's growth, since the rest of the mite-infested leaf portions are still photosynthesizing and benefitting the plant.)

Mite and insect populations can fluctuate from year to year based on a variety of factors, but intervention is not needed (nor would it really be effective unless using a pesticide, which we would not recommend) for the sake of trying to prevent them from returning in the future.

Miri