There are at least two companies that make push-on connectors. These seal with an internal o-ring(s) and use teeth to hold it onto the pipe. One brand is Sharkbite and I think the one you have is made by Watts. This is possible because the OD of each is the same. On the pex side, it also has a sleeve that goes inside to hold it snug, keep it round, so the o-ring can seal and the grippers can hold it in place. At least on the Sharkbite (don't know about the Watts), these are approved and pass codes. On a production basis, it's unlikely they'd be used because of their cost, but are much cheaper than hiring a pro to make that one connection.