Cant do revs without road speed unless hes gonna sit revving the !Removed! off it. So its everything to do with it.
Your initial advise was wrong.
I've never seen a guide that says keep under a certain road speed, how can they, all cars have different gear ratios and different engine speed limits. The guides work off engine revolutions.
You can drive at 60 in 3rd, 4th and 5th.
Which do you think will be revving more?
Doing 80mph in 5th is less strain on the engine than doing 60mph in 3rd.
He/she looks at your advise and they think, it doesn't matter what gear I'm in, I'm not doing over 50mph.
As I say, it's all about revs.
You look at any guide on running a car in, they talk about revs, not road speed.