I think the answer is "if the pack fits, wear it." I don’t know if the pack will fit your friend and you don’t know if the pack will fit your friend. Your friend has to figure out if the pack fits — and trying it on is the only way. Can you/he find the same model in a store?

It’s not out of the question. Some years ago I purchased my Eagle Creek pack from REI online. Mistakenly they sent the women’s version. Having thoroughly examined, been properly fitted, carried under weight the intended pack at a local and very good outfitter, I knew the difference, but I seriously entertained keeping the more trim bag. The defining differences are a narrower profile, closer shoulder straps, smaller waist band, and slightly reduced capacity. Height is less a factor than torso. Your buddy needs to actually try this particular pack as well as comparing it to others to find a suitable fit and something personally, acceptably satisfying.