The same phenomenon that can occur on tomatoes -- adventitious roots -- can occur on other plants as well, including rosemary. They sometimes form in response to high humidity or even exposure to certain herbicides, but it can be normal for them to appear for no apparent reason and stop development before forming functional, normal roots. (They'll remain dark bumps like this.) They aren't harmful to the plant can do not have to be removed, though if you did want to remove them, you can't scrape them off or cut them out; the entire branch just below that point would need to be pruned off. (Incidentally, you could try to root if afterwards if you wanted.)

The plant looks good overall thus far, so just keep it in full sun or a mostly-sunny exposure and make sure the soil doesn't stay damp since rosemary, like most Mediterranean herbs, has limited tolerance for evenly-wet soils or poor drainage. (You can feel the soil an inch or more deep into the pot to determine when to water. It can become somewhat dry to the touch at that depth before watering will be needed, though bone dry for too long should be avoided.)

Miri