The article describes this as"prop money", but doesn’t give further details.
If you’re curious, Adam Savage has a number of videos from Hays Press explaining actual prop money.
https://www.youtube.com/watch?v=drLzVcgnBfI
https://www.youtube.com/watch?v=EfYcSqxh1GU
https://www.youtube.com/watch?v=UlrX1btOH7Q
That must be a first. At least, I’ve never before heard of a seal on an airplane…