I didn't think it was that strange, though I do wish Cheren would've kept his to kind of dilute the whole "glasses are nerdy" thing they had by only making Bel get glasses after she became a scientist. (Although... since Cheren now runs a Gym that is also a museum, maybe it would've just been worse. 'xD) But anyway, yeah, I don't really think it's that surprising... some people change between glasses and contacts every day depending on their mood, so it just made me assume they both had poor eyesight from the beginning, but Cheren didn't want to deal with contacts while he was traveling but can wear them now that he's working indoors, and Bel always switched between glasses and contacts but wears the glasses in BW2 because her outfit in BW2 is more casual.