The truth is likely that the laptop wasn't real, but some of the data was. It's easy to grab some personal data from someone (say, via their actual computer after it's been hacked) and then load it onto another laptop. Then you claim that this laptop was the actual source of the data and that it being abandoned gave you the right to look through it. (It doesn't.)

The must insidious part of this is that you could mix fake data alongside the real data. Got Hunter Biden nudes from your hacking? Toss them in an "email" that he was sending and then write up another email which "proves" that Joe Biden sold his position for personal profit. The nudes email can seem legit enough that it raises the believability of your "smoking gun" email.