it only popups when there more than ~500ms between touch-down and touch-up and almost no touch movement between down and up.
But on very heavy tours on slow devices when the framerate drops down to a very low rate for some time, the system/device itself can become so low, that normal touches are already matching these conditions.
During writing this here I've got an idea - I will try increasing that 500ms wait-time depending on the current framerate - that means to wait longer when there is a low framerate. This should avoid an unindented opening of the contextmenu.