"Zero Knowledge Encryption" is just a marketing term...
I wish marketing would not cross wires with real crypto, it makes me skeptical that they really know what they're doing. They're not the only company doing this and they should be called out for it like spideroak [1].
ZKP[2] is real branch of cryptography and they do not use it AFAIK.
[1] https://spideroak.com/articles/why-we-will-no-longer-use-the...