His words may sound harsh to you, but they are nothing when compared to what Buddhist scripture actually has to say on Muhammad and Islam. You can read the paper here (Vol. 21, No. 2, 1998), and below is WikiIslam's page on the subject (visit the original page for references):
"The Kālachakra Tantra is a 9th century Tibetan Buddhist text that contains passages which discuss the religion of Islam in a negative manner and refer to a man named Madhumati (i.e. Prophet Muhammad) who would be a "false impostor, wreaking havoc" on the Buddhist world.
Like the Hindu Bhavishya Purana, it describes Muslims as invading "barbarians" (Skt. mleccha, from two words "Malina" meaning lowly, dirty, filthy, impure, wretched, unchaste, unclean, admixed, adulterated, contaminated, corrupt, immoral, decadent, infected, obscene, tainted and "CCha/CCheetkara" meaning abhorrence, loathing, disgust, abomination, repugnance) and contains the prophecy of a holy war between the followers of Islam and Buddhism.
It refers to Islam as "mleccha-dharma", the barbarian religion, describing it as a religion of violence ("himsa-dharma") that advocates savage behavior ("raudra-karman"), and characterizes Allah as a barbarian god, who is a merciless deity of death ("mara-devata"), a god of darkness comparable to Rahu, the demon who devours the sun and the moon.
One passage of the Kalachakra states that the powerful, merciless idol of the barbarians, the demonic incarnation (i.e. Muhammad) lives in Mecca. Another reads, "The Chakravartin (i.e. universal ruler) shall come out at the end of the age, from the city the gods fashioned on Mount Kailasa. He shall smite the barbarians in battle with his own four-division army, on the entire surface of the earth."
According to Professor John R. Newman, a historian of religions who specializes in Indian and Tibetan Buddhism, "We may summarize the Kalacakra tantra's perception of Islamic beliefs and practices as follows: from the Buddhist point of view Islam is demonic and perverse, a perfect anti-religion which is the antithesis of Buddhism".
Similarly, the late 14th century Uighur Insadi-Sutr also contains Buddhist denunciations of Islam, describing Muhammad as evil, and expressing messianic hopes that Maitreya the future Buddha would soon return and even win over the kingdom of Baghdad."