Short answer: Yes, in healthy volunteers psilocybin was associated with a temporary reduction in cerebral blood flow and a narrowing of the internal carotid artery. The pattern is consistent with involvement of 5-HT2A receptors, since psilocybin is an agonist and the 5-HT2A antagonist ketanserin did not show similar effects, but this is not definitive proof of mechanism.
In a single-blind, cross-over MRI study of 28 healthy adults, higher plasma psilocin levels and stronger subjective intensity tracked with lower regional and global blood flow, averaging about an 11.6 percent decrease at peak, and the internal carotid artery diameter fell by about 10.5 percent; ketanserin produced no significant changes. You can read the study summary here: study.
These are acute physiological findings in healthy participants and do not speak to clinical benefit or harm. They suggest a 5-HT2A-mediated component, but other factors could also contribute.
Hope this helps clarify the question.