Hey i'm pretty new to this whole thing so excuse me if i'm pointing out something obvious.

I'm guessing the rule should be updated since the game now ends after the button is hit 2 times ?

If I recall it does take 3 hits to beat the boss normally, but to make the fight faster you use portable truck as your second hit to skip the last one. I'm not positive about it though.

Just played trough it, the boss now only takes 2 button pushes.

we use the truck at the first hit, and effectively , each time, I played the boss (legit), I only need 2 hit

Is this run using a specific game version ? If not just beat the last level in the latest steam version and you will see that the boss only takes two hits without pushing the button with the extra truck.

Yeah it needs updating. It's only two hits.