That's right. It's a Uponor PEX fitting.
You will need to cut the tubing and then reconnect them.
Attempting to remove copper pipe from water lines which are plastic. The problem is I cannot separate them. The copper pipe will turn freely but will not come apart from plastic fitting.
Except you will need to have the special tool or homeowner connector device ready before you cut.
Normally a water heater has 24" of metal piping before you convert over to PEX or CPVC.
Being that is the case, we use 24" flex connectors, either copper or stainless steel. Not the braided supplies, but the corrugated supplies.
Those flex connectors are really the DIYers friend when it comes to water heater connections to any kind of pipe!