I think any sort of safety-related recall is going to be a net PR loss for Tesla. Immaterial means the cost is irrelevant, not that it's low. I don't see any evidence that it's anything more nefarious than what they're claiming.
> An item is considered material, according to the American Accounting Association, when the knowledge of it would influence the decision of informed investor.
http://simplestudies.com/what-are-the-exceptions-to-basic-ac...