I guess the key here is, that Tesla knows that that OSM isn't "trustworthy"[1] and consequently treats the map information as it should be: just as the source for the routing algorithm. So it uses the maps as the basis on how to get from A to B, but the actual driving is based on the sensors, not trusting the maps. So the worst case of false mapping information would be of trapping the car in a place where it doesn't know how to get to its destination.

[1] Due to its open collaborative nature, there is an obvious risk for bad or even malicious edits submitted to OSM. On the other side, "professional" and closed mapping services can have errors too, especially they run the risk of being outdated, so shouldn't completely be trusted either. Due to the community efforts, overally the OSM data should be better maintained and errors can be fixed resulting in better map quality. But the big thing is, that you cannot trust any map data 100% - and if only it has been invalidated by a tree falling onto the road.