The challenge in the photo below is that the gutter has a double leaf cover-the heavy diamond screen to keep out large leaves and heavy sticks; and the fine screen to guard against small seeds. This renders the Gutter Guard's leaf guard hook (see it in the photo above not being utilized) useless, as the user can't penetrate the hook through the heavier diamond gutter guard and "hook the gutter for safety" due to the "seed" screen. So, you can see how the user moved the ladder over to a roof vent to tie the lashing strap around it to crudely tie the ladder against the gutter. The significant accomplishment here is that tying the ladder against the gutter enables firm attachment of the ladder against the rubber gutter grabber blocks, which mitigate any force within the 180 degree hemisphere toward the roof side of the ladder. When the user leans his weight on the rails of the ladder to mount and dismount the roof, he is pushing his weight down against the rails of the ladder, causing the rubber gutter grabbers to keep the ladder from sliding against the gutter's edge.
Grant it, the vent pipe can only stand up against so many pounds of force in the unlikely event of a kickback or fallback scenario, and may not completely withstand the full weight of a 200 pound person falling back into the ladder. However, the probability of a full force fall is unlikely due to the fact that a lot of weight from the fall would land partially onto the roof itself, with only some of that transferred to the ladder.