YES the Weaver/Picatinny rail portion IS PLASTIC. It is a strong glass fiber(?) reinforced structural polymer and is NOT metal. Therefore it "may" break under scope clamp stress and the repeated impacts of the springers (although milder gas spring) double recoil. You should be aware of that possibility before making the purchase.
I also read some complaints about rail breakage and would NOT have purchase this at the NEW price. A ~$51 refurb cost makes this a bargain project rifle for me, with really nothing to fix other than that crunchy stiff trigger and safety. I LIKE shooting open sights so if the rail were to crack on my rifle I think it would remain 100% functional for my use.
Also remember that the "squeaky wheel gets the grease". For every broken rail complaint angrily published (as they should be) there may have been thousands of quietly satisfied customers?