D3 slow acceleration (turbo not turned on?)

[AlphaScorpii]

Volvo C30 2012. automatic, D3 150PS, 143000km.
Today I realized driving through the city that car was accelerating slower then usually, specially in higher rpms (when I would put the pedal all the way down). Normal driving up to 40-50kmh with pedal pressed 20-40% I didn't feel any difference. It felt like turbo was turned off.
I went to my service guy, he put it on some diagnostic, reset everything and now everything is fine. He said that through that diagnostic, he can't see the problem.. that I see how will car behave and if same problem will happen, he will phisically check everything (he is busy now with other cars so couldn't take mine for whole diagnostic).
Anyway, I was wondering what could be the problem?
Thing that comes to my mind is that maybe I am driving car too slow (very rarely in high rpms for longer periods.. my pedal is most of the time on 20-40%) and somehow that could cause the problem? I am driving slow mainly because roads in my city are bad and I am on coilovers+18" wheels so I am trying to avoid potholes etc..