"Interval between three pitches" is not a well-defined concept, just like "distance between three points" isn't. You need additional qualifiers to describe what you mean by that. Maybe you want the shortest path between them, or maybe you want a triangle. In any case, using a term like that makes it seem like you're confused with the terminology.

They are questioning jancsika's assertion at the top of the thread that an interval can somehow contain more than two pitches:

> An "interval" is the difference between two (or more) pitches.