Not exactly, partly true, later shunga dynasty supported buddhism as well. One has to look at the same sources that , the first state sanctioned genocide on basis of religion infact happened under Ashoka . so it was ashoka who used violence, then new empire that displaced them also used violence and since buddhist sangha was associated with mauryan empire a lot, they too suffered probably, but then again, the next generation also supported buddhism. Later period of attack by mihirakula was defeated by other hindu kings who were praised by buddhists in their writings. Infact, ambedkar writes buddhism disappeared because of coming of Islam.

“There can be no doubt that the fall of Buddhism in India was due to the invasions of the Musalmans. Islam came out as the enemy of the ‘But’. The word ‘But’ as everybody knows, is the Arabic word and means an idol. Thus the origin of the word indicates that in the Moslem mind idol worship had come to be identified with the Religion of the Buddha. To the Muslims, they were one and the same thing. The mission to break the idols thus became the mission to destroy Buddhism. Islam destroyed Buddhism not only in India but wherever it went. Before Islam came into being Buddhism was the religion of Bactria, Parthia, Afghanistan, Gandhar, and Chinese Turkestan, as it was of the whole of Asia.”

decline of buddhism