With the picture I saw from the link you provided, this should not be advisable because it looks absurd, miners like GPU do hot to the extent it has set some mining farms ablazed. it will be dangerous to use car to mine, I mean having the mining rigs inside car. It can be that the battery can power it like it is said in the OP board but what about the hit, it is good for us to not risk what we know can be dangerous. Mining should be done in the official way, to use ASIC is the best, only ASIC can mine bitcoin now, GPU will only lead to loss and not advisable.
I don't think that the miner drives his car while mining.
I think he did it for fun because he is tech-savvy, and that idea comes from a joke by someone in his community.
It can be experimental purpose too, to show how good or how powerful Tesla's electricity, so it used for crypto mining to prove it.
I also think that it can be promotional material by Tesla to join the bitcoin hype in 2017, since the "When Lambo" thing still correlated with bitcoin hype that year.
plus, If I am not mistaken Tesla's owner can get free electricity on the Tesla station.