Do you really think that could account for it?
Isn't it more likely that Tesla's range claim is just incorrect?
Yes, I do. Continental isn't a stand-alone tire company like Michelin, Bridgestone, Yokohama, Sumitomo, etc. They are owned by some other tire company (they used to change owners every couple of years--don't know if that's still true). So I don't expect Continental to have the latest tire technology, and newer technology certainly can make that kind of difference.
Of course, Tesla could have made a mistake or the conditions of the test were different. There's a lot we don't know about how they did their evaluation.