Reddit is an interesting case, but I'd say there's a categorical difference between faking that you are able to do something you can't (Theranos) and pre-filling a functioning site with content (I assume that's what you are referring to?).

It's especially relevant if the difference actually matters for whom you are tricking: If the results had been accurate (which from what I understand they weren't) and absent any other specific claims of superiority Theranos end-users wouldn't care about what tech they use, but for investors relying on claims that they can do something others can't to establish their value it obviously does matter.

Which in the case of reddit I guess makes the question: does it make a material difference for users if the site they enjoy is entirely fed by an organic community, or is the most important thing that the site is enjoyable regardless of origin? I guess you could argue that faking a community is also "faking that you are able to do something you can't".