That link really doesn't have any info how to do it. Most it says is the points only move along their radius line, but nothing else on how to make it match agario. The link to code is broken. It looks slightly different. Maybe the secret is to do a full on collision response between points and edges, so maybe another day.
dropbox.com/s/ek59bdqrq71579v/blob_squish3.c3p