I'm willing to give BM a pass on the ability to describe the color of SM's bike helmet and her bike clothing until and unless someone in a position to know indicates that SM had multiple helmets and multiple biking outfits.
I only have a single bike helmet and it isn't unusual for a person to have a single biking outfit that is laundered frequently. Maybe it was the same with SM, so even without seeing her, BM would have been able to reasonably assume what she was wearing.
IMO, it's the many things BM didn't describe about his missing wife that are more troubling - age, height, weight, hair color, eye color, trim vs. not, common biking habits (preferred trails, did she ride on the right side of the road for biking, what time of day did she commonly ride, does she listen to music on earphones while biking), etc. He kept A LOT of pertinent information under tight control.