@Cain1412 - I’ve found some ‘spare parts’ under the front seats in a previous VW I owned from new - a spare bolt like yours and a spare plastic end cap for the passenger seat runners. I always assumed that the production operative fitting the seats and seat runners in the car when it was built took too many fixings into the car and just left them there rather than used them on the next car on the production line.
So maybe that's what happened when your car was built?