That's definitely something fungal... don't take my word for this but I apple cider vinegar will help? Those bumps usually happen around winter time I have heard.
This may or may not help if you're willing to try;" Vinegar is a proven method for destroying mold and eliminating pesky white spots from your plants. Mix two tablespoons of apple cider vinegar with a quart of water, and spray onto your infected leaves and stems. Repeat every few days until all traces of mold are gone. "