Who said that was intentional though? It could easily of been loose skin for a selkie theme or setting up Popplio3's frills or even just be there because it'd look plain without it. Also, iirc, other performers wear similar collars.
Also, acrobatics = acrobat, not clown. Same with the bubbles, which are Popplio's 'props' for its acrobatics.
It's easy to say in hindsight what it's for now that we see the evolution but the way it looks just on popplio is extremely similar to how it looks on clowns, especially with it being frilled. I know acrobats are different, but that's why it seems like it was going for a general theme.