I for one wasn't surprised, it was bound to happen.
Two things -
First, this violent and chauvinistic branch of Hinduism isn't anything recent, but has been around for a long time.
Secondly, it was only a matter of time before some loon take law in his hand to avenge what they see Govt appeasement towards minority groups.
I don't understand the statements like Hindus can't be terrorist, probably people try to mean that Hindus can't justify terrorism using their religion as the concept of infidel and holy are alien to Hinduism, once again the answer lies in the particular branch of Hinduism which shaped in early 19th century and tried to organize Hindus just as Semitic religions do to their followers.