It's only wheelsucking when you don't do your fair share of the work.
In those circumstances in the final 40km, Stannard's fair share of the work was virtually zero. It wasn't any old three riders from any old same team - it was flippin' Boonen, Terpstra and Vandenbergh from the team which wanted it the most. And I expect Stannard was feeling strong enough not to be too concerned about being unable to deal with the chasing group if it caught them - the odds were already stacked against him with the Quickstep triumvirate.
What's more, the three riders were trying to work Stannard over by leaving gaps here and there for him to close and then launching the inevitable attacks, so there was no onus at all on him to contribute at that stage.
Definitely not wheelsucking, but a brilliant display of strength and tactical sense in what should have been an open-and-shut case for Quickstep. Lefevre is just embarrassed his team cocked it up, but probably also admits to himself that Stannard was just too strong anyway.