That's one theory. It's not the only one. I can't say one way or another.

I am skeptical of claims based on speculation.

Plants appear not to have brains. They nonetheless communicate and react to each other's messages. That is behaviour that indicates something other than the brain is involved in consciousness too.

There's a lot of research now ongoing regarding how our gut flora affect our mental state. This, when verified (which it will be) also indicates that such ecosystems effect consciousness, and definitely has no brain.

I'm not convinced brains are necessary for consciousness.

After all, I've met some people that seem to lack the former yet possess some simulacrum of the latter =p