I don't know enough about biology to comment on their storage-density claims, but as to the encryption, I'm getting a strong whiff of snake oil from "only the client would know the function to derive the checksum". If you want to convince me that bioinformatics has something to offer cryptology, then you need to explain to me what property wetware has that silicon doesn't which causes it to be unlike a classical Turi…
The mass of a single base pair is about 1.08E-21 grams. That's 1.85E10^21 bits[1] of information in a single gram of purified DNA, about a forth of a zettabyte. So, if they're using DNA as the storage mechanism (the slideshow linked in the article indicates that they are), then 90GB is pretty insignificant. Sure, the bacteria will all be pretty filled with DNA, but it's not especially outlandish. Throwing compression at the information (as the slideshow discusses) makes it even less outlandish.
[1] Each base pair encodes two bits, as DNA and RNA is basically a base-four sequence (when we're thinking about it as data storage).