Not so. The draft from a bike easily extends back as much as three bike lengths. These are MotoGp machines, not bicycles.
I watched as well, I am sure Petrux was in a position to get a tow and it benefited his lap time, cf the ridiculous spectacle in moto 3 at one stage when pretty much the whole field was dawdling around waiting to grab a tow, and the tow sign Lorenzo's pit crew Lorenzo's tow had at one time to warn him when Bautista was in the vicinity. Team-mates also sometimes deliberately give tows to help the other rider on the team.
Slowing the lead rider down not so much though I hadn't thought, most of the chagrin has always seemed to me about the following rider benefiting from the work of another, being in a position to copy the lines the lead rider is employing etc.
If Petrucci waited around to get a tow which I didn't see Dovi might have cause for complaint since the tow allowed Petrux to set a time which he may not have been capable of on his own which kept Dovi out of Q2, but of it was happenstance not so much, particularly since it was for 1 lap and qualifying is part of racing as has been said, with the larger problem being Dovi scrabbling around in Q1 in the first place.
Further evidence of the level of dysfunction in how Ducati run their motogp teams (it has mostly been thus since they entered the premier class), they have a contending rider who is not signed for next year and a second rider also not signed and hence have no leverage on either, both making no pretence about being disgruntled, saying what they like publicly, and it would seem not overly fond of each other either.