Seams on hypalon boats are glued. They appear much flatter in profile than PVC boats. The seams are simply overlapped and glued. Check around the seams and you will most likely see traces of excess glue that has seeped out. Hypalon boat manufacturers use a 'contact cement' type of glue in their seams. PVCs are not glued.
Seams on PVC boats are heat welded. They are 'thicker' in profile than Hypalon boats. Often the seams are covered with a strip of material which makes it difficult to see the heat welded seam. But look around to other areas of the boat and you will most likely identify the heat welded seams. See photo
Find a small area on the boat that is hidden from view and apply a small amount of MEK (methyl ethyl ketone), Acetone, or Xylene on a rag; and rub the test area.
If area becomes sticky, if the top colour runs, or the surface of the material feels tacky, then the material is most likely PVC.
Hypalon will leave an oxidization and maybe some colour on the cloth; but the material will not be affected.
If you can see the inside of the tube (through the valve) - Hypalon is a dark grey or black on the inside. PVC is the same colour on both sides.
Lightly sand the material.
Hypalon will matt down and produce a dust.
PVC will just scratch. There will be no difference in colour.