From what I can find, an average sweater uses between 3-6000 feet of yarn [1]. Apparently an ‘ideal’ altitude for for skydiving is 14000 feet [2]. That puts you around the same altitude as high altitude aerostat radar systems[3]. It would have to be a fairly voluminous sweater, but it’s probably just about within the realms of possibility. It’s chilly at that altitude, so maybe it was made with several layers for extra warmth?

I’m no wool-ologist, and even less of a jumper out of planes, but these were the sources I used to get my figures:

[1] www.blackeryarns.co.uk/…/wool-ball-lengths/ [2] friendlyskydiver.com/skydiving-altitudes/ [3] en.wikipedia.org/…/Tethered_Aerostat_Radar_System