Are those what they call leaf galls?
I think you are spot on there. Which is better news than some other possibilities.
I found the following info on thespruce.com
Whatever the original cause, these organisms are usually not still on the leaf. The gall itself is the plant’s response to the irritation. It’s not unlike the bump you get when an insect feeds on you, except the leaf gall is not going to go away.
Despite appearances, the insect is not living in the gall, and it has left behind no eggs in the gall itself. It is very likely that once you notice the galls, the insects have moved on. Before they do, they can do a lot of cosmetic damage to many plants and in particular trees. Galls can also form on stems and flowers. However, leaf galls seem to be the most prominent and get the most notice.
It is almost always the fresh new, leafy growth that is attacked by the insects and other organisms which results in the presence of galls. Mature leaves are rarely affected. However many common trees are susceptible to leaf galls, especially when first leafing out in the spring.
Damage will be more considerable following a mild winter since more insects have survived and are hungry. That is true of any insect problem in your yard or garden. While the damage from galls won’t usually kill a tree, it can weaken the tree and may cause early leaf drop. A
healthy tree will send out new growth and recover, but the loss of leaves and photosynthesis will weaken a stressed tree