6th gear..

I know at 70mph the car revs to around 3750 I was driving my dads 1.6 Alfa 147 today and noticed that it revs to 3,500 rpm at 70mph in 5th.. the thing is there was no noise.. so what makes the Clio so different? is it because of how the engine is designed its nosier?
 
I know at 70mph the car revs to around 3750 I was driving my dads 1.6 Alfa 147 today and noticed that it revs to 3,500 rpm at 70mph in 5th.. the thing is there was no noise.. so what makes the Clio so different? is it because of how the engine is designed its nosier?

Gear ratio, exhaust...