In this instance, it would be more than "look and feel" and more "would a person assume this project is done by the original Factorio developers" — are they misleading the audience. They copied much of the UI from the Factorio site for instance — so if they wanted you could make the argument the intent is to mislead.
I think you’re confusing trademark and copyright. Trademark is about confusing the public. Copyright is about derivative works. It seems pretty clear to me that this is a derivative work, due to its direct copying of Factorio sprites.
The website UI is by the Alt-F4 team, not the FUE5 team, it's like seeing this discussion and then complaining that FUE5 'copied' Factorio's colour scheme, thinking they are also behind hackernews, lol.
