Yes, I know the main page mentions that it's an unrestricted free license, but that's not actually saying what the license is. There's a price tag on the engine, so it's clearly not copyleft. But the only thing I can find anywhere in the files is the license information for the dependencies. There's even a message at the top of that file discouraging people from actually reading it.
How can you call this a "professional grade" engine and not tell people what they're allowed to do with it? Admittedly, I would only be interested in a making a game with it and perhaps selling the game, but that's only because I'm not sure the engine is easy enough to use. Just last week I came to the understanding that it was fine, according to the license, to hand a copy of Pico-8 to a relative that lives with me so she could dabble in it a bit. I can't tell, even after scouring all the files, whether that'd be legal for me to do with this engine.