Personally, I am not hesitant to label anything because of my "if the hat fits..." and "if it walks and quacks like a duck..." conditioned, biased upbringing.
That being said, what is being talked about and experienced here, sounds a lot like the Chakras and the visual representations thereof.
A red triangle (usually inverted) symbolises the Muladhara or the root Chakra.
Meditation teachers usually give visualization methods with associated shapes, colours and sounds (bija mantras) to bring awareness to the Chakras.
Seeing a red triangle in the astral could be associated with the need to ground oneself, bring the awareness out of the Third Eye (Astral Realm) and back down to earth to balance the energies out.