I think a little piece of me just died...

Today's lesson:
Using "that" as a conjunction. For example: you know that, you hear that, and so on. As if teaching extraneous words wasn't bad enough (I'm a fan of removing any excess "that" 's in writing), today's dialogue was as follows:

Guide: Of course, you know that dolphins aren't fish. They're animals like us. They live about 20 years.

Aki: What do dolphins eat?

.
.
.
.

and later:
A: Dolphins are animals like dogs.

B: ...

A: Do you understand? I said, "Dolphins are animals like us. They aren't fish."

Wait a minute -- don't you mean mammals?!? I mentioned it to my JTE, but because it's in the textbook (written by non-native English speakers), that's the way it is. Dolphins and dogs are animals. Fish are fish. Dolphins are not fish. Do you understand? Wakaru?

Does this mean fish are not animals?
Do I have to turn in all those Biology degrees now?