Sea lions are related to canines, and given that canines are empathetic, it makes sense. 

Also, if I learned anything from The Little Mermaid is that under the sea is a musical place.

He's got rhythm. Who could ask for anything more?

Backstreet's back all right! Boogey wonderland!!

That's awesome, but did they just train her?  How can you tell if she's just not using the training and not actually feeling the beat? 

Reminds me of Clever Hans. http://en.wikipedia.org/wiki/Clever_Hans

In the video they said they'd noticed her doing it on her own, and she changes her bobbing to the beat, which if it were just training and not beat keeping she'd likely only move in the same way, and not in rhythm to the music.

Plus, she's isolated when they're observing her, so she's not responding to any human cues about how she's behaving.

She just has natural rhythm!