I think he is trolling, with just enough information to sound correct. The Keccak authors have proposed a "duplex construction"[1][2], using the arbitrary length inputs/outputs and the lack of a output transformation in the sponge construction, that could be used for authenticated encryption. The NIST has yet to included that use case in the SHA-3 standard. So, until there is enough solid understanding for its correct use and tested implementations with that use, it is just a hash function.

[1] http://sponge.noekeon.org/ (end of the page)

[2] http://sponge.noekeon.org/SpongeDuplex.pdf

...no

Keccak is a generic construction suitable for more than just hashing. Here, let me copy the first bullet point off their site.

> As a sponge function, Keccak has arbitrary output length. This allows to simplify modes of use where dedicated constructions would be needed for fixed-output-length hash functions. It can be natively used for, e.g., hashing, full domain hashing, randomized hashing, stream encryption, MAC computation. In addition, the arbitrary output length makes it suitable for tree hashing.

Note that Keccak has a significant amount of hidden state, and they proved that the sponge construction itself is secure as a function of how many bits are hidden.