Yes. But one has to count the networkeffect. A person with 100mio followers can assume that every post is copied screenshotted or something. An account with only a million followers, can probably say that there is still the possibility any comment could be fotograpfed. But an account of 10k followers or less is probably very unlikely someone would care to screenshot every shitpost. And this with snowden has nothing to do with this. Snowden is concerned about state surveillance. So he talks there rather about technical implementations of deletion. But this does not matter, when the owner of the storage has no intrest in recovering the information.