Motorcycles in your bus lane

(now playing devils advocate....in a very nice suit of course) By your own admission not breaking the speed limit. Also, sort of, riding within accepted guidelines given by the IAM (not filtering at more than 20mph than the other traffic).

Would your opinion have been altered if it had been a cyclist riding at 25mph in a similar circumstance?

Why should it be altered? If you're conveying a vehicle of any kind in a manner that doesn't take into account current road conditions then you're a danger to yourself and everyone around you.

It doesn't matter if you're riding a bicycle, a motorbike, a car, or a rocket-propelled donkey. God help us all if nobody is able to read actual road conditions and say "but the IAM says what I did was sort of ok!" instead of taking responsibility for their own safety.