That may not be far from the truth.
I’ve often wondered what would happen if we showed them movies underwater, movies that were specially constructed to convey info to them.
If their trainers name is Bill, show them a picture of Bill and have a speaker say “Bill”
See how they respond.
Show a picture of a fish and have the speaker say “fish”.
I would bet dollars to donuts that we could start breaking the language barrier that way. Dolphins are highly intelligent, extremely inquisitive creatures.