If anyone, anywhere, in the loop is doubtful it should always be queried - remember Tenerife.
The reason the clearance was given this way possibly relates to the way the system works at Maastricht. On initial contact with a sector the flight is assumed. Amongst other triggered actions this can briefly display the route of the flight through the Maastricht airspace. As this is only displyed for some seconds the route - direct where possible - tends to be given first.
I agree the confusion could be avoided by using the phrase, "Continue climb" or "Climb now".
Lon More, here since before Pontius was a Pilot or Mortus a Rigger