Structure of tomato, ginger and garlic after blending in a blender
I suspect the culprit is the tomato, which does a good job taking on air and looking 'foamy'. I've noticed this if I use my stick blender when making pasta sauce from a few jars of canned tomatoes as well as when I make gazpacho. Even a few short bursts in a blender can whip up the contents. 

A food processor, which typically has a flat blade, won't incorporate as much air as the blender, rather it's going to chop vs. whip. 

Also, love how you asked about 'why' vs. expressing disgust at the result. Probably makes no different in the final result as the heat of cooking will take care of the foam, as will time.