you say this happened and then when you took him to a pet store he responded appropriately to another dog with no issues. Doesnt sound to me like you have anything to worry about honestly. Sounds like he recovered quickly and is no worse for wear.
The more people I meet and talk to,the more I love my dogs and their intelligence.
Zena GSD 6/1/03
Shasta GSD 5/5/10
"Dax" Thor z vom Weberhaus GSD 3/18/2013
Riley GSD/BC 1/10/05-2/1/2013