Is Huayan Buddhism the one that teaches about infinite universes being held on a jeweled flower garland, or is it another branch/sect of Buddhism?
華嚴 (Hua-yan) literally means "flower garland". The name is the Chinese translation of "Avatamsaka". The name Flower Garland is meant to suggest the crowning glory of a Buddha's profound understanding of ultimate reality. The Avatamsaka sutra contains the following verse:
In each dust-mote of these worlds
Are countless worlds and Buddhas...
From the tip of each hair of Buddha's body
Are revealed the indescribable Pure Lands...
The indescribable infinite Lands
All ensemble in a hair's tip [of Buddha]