You also need to compare Tesla aluminum-bodied cars with aluminum-bodied cars. Which are more expensive to repair. The IIHS article doesn't say what cars they compared Model S to, and aluminum-bodied cars are rare enough that it's likely not very comparable.
Mind you, that doesn't affect the claims-per-mile statistic.
And the Tesla is furthermore an outlier, because for a long time it was the only luxury EV in widespread use. In a couple more years, the data on "luxury electric vehicles" should have a lot more data points.
Mind you, that doesn't affect the claims-per-mile statistic.