He definately didn't like something,from the video,it looks pretty windy so it could have been noise. Idon't recall his ears twitching around trying to find the source of a sound,he was looking around alot like he was trying to find something.

My bet is he winded you and with the wind swirling,he couldn't tell where it was coming from.One thing is for sure,when he gets older,he won't hang around that long trying to figure it out.