Yeah, I don’t know how you’d know definitively if it’s PEX. The stuff I buy locally ((Home Depot, Texas) is not translucent like what you’re showing but a quick Google search shows that it comes that way. I don’t know of any other kind of plastic used for supply lines (but I’m not a plumber).

Also I saw a reference to PEX-A and PEX-B….. life is never simple!