I consider this kind of a gray area because bikes really aren't supposed to be on the sidewalk therefore there isn't really a solid rule on which side they should be on. Pedestrian traffic on the sidewalk is not obligated to be on any particular side of the street, that only applies when walking in the street itself. There are a couple of places I salmon on the sidewalk in my commute because certain sections of the road are very bike unfriendly and either the sidewalk is only on one side or there is some logistical reason to be on that side (obstacles on the other side, upcoming crosswalk only on that side, I'm going a short distance and being on that side makes more sense based on where I came and am going..etc). I'd say unless its a big problem you are better off just minding your own business.