Looks like another attempt for attention by some sort of piloted “thing” that is fast enough, large enough, and recognizable enough for 4 pilots to identify these flying “things” as JetPacks. Kudos to the airliner crews who seem to be looking outside occasionally, yet are not looking for specifically JetPacks. So, I would surmise, someone has a flying machine the size, speed, range, and shape to get the attention of commercial airline crews who would not normally be looking for this kind of traffic yet seeing them clearly enough to call ATC with an identity both crews and ATC recognize in a general way.
Plenty of RC lawn mower and Snoopy doghouse replicas flown. With many turbine RC airplanes capable of 250+kts, GPS with all sorts of stability systems on board, and modern drone technology that allows for beyond line of sight flight, I am sure some YouTuber has a RC, full scale, Jetman replica. That would allow for plenty of range, performance capability with even some stealth because of the relative low noise to launch and fly modern RC turbines.
Not saying it was Steve Holland but check out this YT video
https://www.youtube.com/watch?v=sw_I6jpOc3Q