+1. Remember, the speedometer usually reads high, so 275 kph is probably around 255, where the limiter is supposed to cut in.The speed limiter cuts the fuel gradually but effectivley. This causes the car to stop accelerating but effectivley rock between 155 and 157 mph - for example. This is quite gentle but noticeable. It is nowhere near as violent as hitting the rev limiter.
If it were clutch slip im sure you would have noticed it. At those kind of speeds with those kinds of wind pressures I would expect the rev's to be shooting up as the clutch slipped.
I would say that you were on the speed limiter.
My elementary explanation of course.
For the OP, I would check with whoever told you the car was "delimited". If so, it should hit well above 255 kph in real speed, probably 300 kph as read by the speedometer.