Youre right, I spend like 2 minutes looking and found this.
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And exactly as I said, looks
oddly familiar. It doesnt have the same texture decals but the model structure is exactly the same which leaves no doubt, they are using this asset and re-textured some things to make it different. I dont get why the dev would lie about such a thing. I can only pick Wild Life, ProjectH and Slaves of Rome as examples here because those are the projects of similar scope I follow but all of those devs have publicly mentioned they use stock assets for animations and environments. Not for all, but for some, or for prototyping. And I think thats totally fine and a legitimate way of making your development as efficient as possible. You also dont have to mention it because it really isnt that big of a deal, but why lie when specifically asked about it? Like FOW when they lied about their spaceship models for subverse and someone found the exact same ships on some unitiy asset store or so. People will find out and it will make you look very very dumb and dodgy.
Edit: The creator of that UE4 asset pack has a ton of other packs for all sorts of things. Now I havent spent more time looking because I dont really care that much but I can imagine the dev is using more of these things.
In the end its pretty clear, the amount of things the guy already has done is virtually impossible to achieve on your own without some serious funding - or with stock assets.