It's not waterproof, it's water resistant. No way those motors are sealed against water ingress.
No, the motors don't need to be, in fact they need airflow to stay cool. We just seal the electronics on our RC gear, and hose the salt water out of the motors when we get home.
As you said Harrow in the FAQ they say if you immerse it in salt water, be sure to rinse the motors out with fresh water after use.
What will the selfie generation come up with next?
An annual selfie awards show, the trophy could look like a gold plated hand mirror with the inscription of something like "you're the best", depending on the category of course.