You may be correct on what that is. It may not have been in correctly. Since neither of you new it was in there it could have backed off the back and the spring may not have been in it evenly. Idk for sure but possible.
Check to make sure the carrier key is not bottoming out on the ring of the lower receiver where the extension screws into. Split the upper and lower, pull the bcg and then push it down the extension and see where the bcg stops with the spring and buffer in the extension. That piece will have changed the depth of the extension. Look at the ring and the back of the carrier key too for the finish to rubbed off in a rectangular shape. It may be referenced by some that the bolt face should be up to a 1/4" ahead of the rear of the ejection port but that really doesn't matter as long as the bcg isn't bottoming out on the receiver.