Elon Musk talked about how BTC mining with electricity isn't environment friendly but he invented electric cars, in near future if this actually becomes popular electric cars will be available world wide and billions of vehicles will be charged by electricity so how is this environment friendly?
That's the irony or contradictory about Elon, and about this statement on bitcoin mining, it has been debunked by many experts so we shouldn't believed or be influenced on anything he said on his twitter account.
He simply wanted to gain attention and create a lot of FUD, but in the end, I think he will not succeed because it's obvious that he has some narrative behind his attacks on bitcoin and bitcoin mining.