I had Jesse do that at about 5 weeks. None of my babies were ever really spewers, so seeing a whole feed come back up like that scared me!
Does he do it after every feed? Jesse only did it once. The reflux I've seen is after every feed. DD2 had slight reflux & colic, but not enough to worry.
I'm sure there are plenty of reflux mums on here who know alot more about it than me!