This may just be semantic games, I don't really care about a marketing pitch. I thought I was bored enough to participate, but I guess wasn't, so the below is incoherent. I'll post it anyway.
Survival being all things related to health; heat, nutrition, disease, wounds, maybe strength(/conditioning/stamina). Describing a game as "partly a survival game" would imply that there are elements of the above, but they're not all that significant.
Describing a game as a "pure survival" would mean that most of the gameplay is focused on solving those issues in whatever environment the game takes place in. A "pure survival" would essentially require a hardcore approach, which to me implies a "certainty of failure - if not skillfully avoided", or something to that nature. To reach "hardcore", survival would have to be an actual issue, something that makes you drop whatever you're doing to solve a survival issue before carrying on. Or having to specifically work for, at least.
As it stands, the survival elements are basically solved by the same thing you'd be doing After solving the survival issues - "just do your trader loop". There's not really anything to do specifically about survival in any stage of the game, it just solves itself by raiding more cabinets and end loots. Day 1, run to trader, make your stone axe and club, get a quest. Find food at quest, eat it. If unlucky, buy food from vending machine at trader. I can't really call that even "survival effort", much less hardcore.
Now, 7dtd is only partially survival, for sure, with plenty of other core elements; this makes it easier to be lenient with the description, but I'd still see "hardcore survival" as an error. It's partially a balance problem, the game could be tuned to get to a hardcore survival feel out of the current mechanics, but as it stands, the solution to all current survival challenges is basically "just do the trader loop".