Non-GAAP is certainly an accounting method. It's especially common for tech companies, because employee stock options are a big cost in GAAP even though the bank account balances don't change.

Also in Tesla's case is their buyback guarantee which is popular in the US market. It's effectively a lease and under GAAP rules that means you don't recognize the full amount of revenue at the time of sale and instead have to do it month by month. That makes a giant difference in revenue recorded even though they have all the cash up front.