It is sometimes, of course, the tone of voice, but I have no problem in being asked if I can manage stairs, or abnormal clasp, or anything similar.
I see that as a neutral, helpful question. More polite than directing someone who might have difficulties via stairs, or automatically fitting a fiddly clasp.
I worked in a field where it was normal for me to check if people could read, could see signs, and so on, so I see such questions as helpful, not as making assumptions.
Regarding looking online, the proper question would have been something like ' are you OK to look this up online? '