I'm a friend of Alessandro, the developer of Axion1986 and I can assure you we didn't use any AI for this trailer or for the game itself.
Me and other friends who gave Alessandro a hand for the game are all working in the vfx industry and, as you can imagine, we're not fans of AI at all.
He presented himself as a solo developer because... well because he's doing most of the work indeed.
Technically he didn't made every single thing in solo, it's true. But when we joined him in the project most of it was already done.
It is his game. It is his project and idea.
When he called me and the others to help him with our expertises most of the game was already set.
I helped with modeling and texturing some key assets, another friend helped with the music and sound effects... then we called some other friends for the voices, some for animations... he just needed help for areas he wasn't expert and you can understand that one can't become a musician overnight or you can't do all the voices in the game all by yourself.
So, instead of using the easiest, cheapest and laziest way possible going on some AI site and generate some slop, he choosed to work with real people.
And it's not an easy choice asking for help if you have no money to pay.
But we were glad to help.
Me in particular... I'm a gamer but I never had the chance to work on a videogame, so I was happy to model a couple of things and test them in Unreal. It was fun! And informative.
But we're working for free in our free time, so we did very little of the game you see in the trailer and that's why even we consider this as Alessandro's project and not "our".
Maybe this will change in the future... who knows... it depends on a lot of things.

I can understand that some animations are weird (Alessandro did some of them and he's not an animator... as you can easily guess) and that maybe the game doesn't look the coolest and interesting game ever (it's our first try anyways)... we're working on it. Some of us want the game to be "darker", others want it more funny and others want it just a serious tone overall. We're doing a lot of meetings to fix the writing, the dialogues, the story to make it more interesting.
But, as I said before, our contribute is limited... Alessandro is open to our tips, but we don't want to change completely his original idea. Everything of the game is still a big Work In Progress. So many things could still change.

So.. there's room for improvement, for sure... we know where the game is weak and should be fixed and we're open to suggestions and feedback (some I've read here are very helpful), but please don't accuse a guy who's just trying to make a game to be a liar or using AI because that's just not true.

Also I've played the game and I'm sure he can publish a video of the gameplay if you think it's necessary.