If using explicit content or dark themes more for the actual shock effect or a sense of cool factor rather than for theme exploration and character development, then it can easily count as edgy.
There is good edge if such events in a series actually contains the latter two points. For example, the Eclipse in Berserk or
are edge done right as they have a permanent effect on the characters. On the other hand, something such as Kaneki's cannibalising power up is completely lacking in substance and just there for the gore, so it can easily count as poor edge.
The example you pointed out is a good one of poor edge since, as you said, there's no way Kaneki should really know about it and seems to only be put in there for a superficial sense of seeming dark.