It does look like a bralette, not a proper top tbh. There appears to be little back to it. I wouldn't have seen it as being proper outwear bar being by the beach, in a club/bar etc. Likewise I wouldn't see a vest on a man as being proper outwear for a plane journey either.
Couldn't she have just through a little wrap or cardi type thing over it - surely more comfortable when sitting on a scratchy material, or plastic 'leather' plane seat anyway.
Maybe Im just old though 