Why would a mechanic crank heater to maximum

This is a curiosity question. I recently had the timing belt, tensioner and water pump replaced on my Honda Odyssey.

When I picked up the van it was really hot inside but I didn’t think much of it. Later I turned on the climate control and noticed the mechanic had set it to 34c and apparently ran it long enough to really heat up the interior.

Is this a standard test of some kind related to either the coolant change or the other items that were serviced? And assuming it is, what is the goal?