I do agree that "target" and "actual perfomance" are different things and it's good to retain a healthy amount of skepticism. Just bear in mind these guys have people that designed most of Apple's ARM cores (even some not released yet), so they are far from being charlatans.
By the way, Nuvia is excluseivly targeting servers only, hyperscalers more specifically. Their people have mentioned that in interviews time-and-time again. (and among other people they even have some working for them that come from Google's custom hardware projects).
I recommend reading
the cited Nuvia blog-post in it's entirety, you'll see that they mention servers multiple times.
They also state quite clearly why they showed ST performance per watt estimates between 1W - 4.5W and why it matters for servers:
TL;DR That's because that is what upcoming 64-128 core servers will have to spend per-core being fully loaded (when being air-cooled).
That quote should also make it quite clear what their target is (250-300W TDP 128 core server).