Ah, obviously the police suspect he's up to no good then. Reading between the lines his bike is able to provide assistance above 15.5mph, "I set my speed dial to 15.5mph", and the police are struggling to prove that.
Remember that we are not in Nazi Germany but in the UK, apparently the land where spot checks, inspections and giving a reason to be doing what you are doing, providing ID isn't compulsory but somehow that hasn't been explained to the police who frequently breach the law.
If you quote the law when stopped this winds them up no end and they will victimise those who question what they say.
The police are a law unto themselves and again i say don't know much about a lot really, they will generalise and bully you into complying.
I do not know what suspicions they had about this chap so cant comment on whether they had just cause but to believe they are all above board is a bit naive.