You added a lot of qualifiers to the simple statement that the skateboard was not Tesla's idea....
You don't have to mass produce something in order for it to be your idea, and GM had the skateboard idea 20 years ago:
The sign reads “our electric future is now” but it should have read “our electric future is 20 years ago.” GM just debuted a new skateboard-style electric vehicle platform for its upcoming EVs, which will sound strange to those of us who still remember GM debuting a skateboard-style electric...
jalopnik.com