He totally believes in it and tells that then he could buy not only a new car but a flat also.
Does it really worth it? He uses his car for his work and now he wouldn't be able to do this anymore as he thinks there's no need to work anymore.
Now there is no need to work anymore? How is he going to pay for food and his bills now?
If he sells his car to invest in Bitcoin, but then takes the bus to work, that is fine. He is just sacrificing a little bit of comfort to invest in something he believes in. Whether or not Bitcoin really succeeds, your friend wouldn't have lost anything.