Perhaps cars actually cost closer to what American and European manufacturers sell them for, and the communist state-backed BYD is the rent-seeking scam that’s dumping vehicles below cost in order to achieve not-quite-commercial objectives.
BYD received massive grants during it's scale-up period, mostly in the form of capital expenditures being fully subsidized or land grants. Very rarely were subsidies/grants awarded for operational expenses though it did happen.
Given the fiscal situation in China it's unlikely BYD will receive as much support in the future but you never know. Green transition is still a massively important political goal in China.
Worth mentioning the scale of support it received is not dissimilar to Tesla which also benefited from very healthy subsidies and tax arrangements with the US jurisdictions it setup in. In fact if you include their $1.3B deal with Nevada (over 20 years though) I think you will find Tesla is in the lead in government money.
Disclaimer: I'm both a BYD and TSLA shareholder
BYD can degrade the US manufacturing base; degrade consumer sentiment (as seen above); put millions of mobile sensors on US/EU roads; etc. It is absolute naivety to think that’s a company that will ever need to truly stand on its own two feet.