Obviously this person who posted this message is unaware of "being harsh with Kuffars and soft with the Muslims (Believers)" Not to say that we have o be harsh with all kuffar...just the ones who attack our honor and our religion. So to answer your question...no it's not a bidah.

Obviously you don't know Islamic history. The prophet (saw) was not always soft and polite towards his enemies when he was attacked whether it be verbally or physically.

“Better to die on one's feet than to live on one's knees.” -Dolores Ibárruri