People collect all kinds of things. The serial numbers may have had some meaning to the buyer....and he/she wanted it brand new right from the print press.
Reminds me of the people that buy original comic books still in their wrapper and never open them etc.
I was in Hong Kong during the handover and they auctioned the number plate HK 1997 for many millions of USD if I remember correctly.
In Canada the new polymer notes were also bought/sold with some fanfare when they were rare/novelty at the beginning in manners like you describe as well.
So far they are holding up pretty well now, except that creases from forced folding tend to be quite permanent (plastic deformation and all etc).
Its the old notes that are quite the novelty now heh. I kept some mint ones of those to sell much later potentially or just pass down to my kids etc.