"Allah" is not exclusive to Islam whatsoever. "Allah" literally means "God" and has literally the exact same function as "god" has in English. Arabic-speaking Christians and Jews use the word "Allah" to refer to the Judeo-Christian god of the Torah and Bible, and Arabic translations of the Bible use the word "Allah." Arabic-speaking Sikhs and polytheists use "allah" to refer to their gods as well. It also predates the Muslim religion by hundreds if not thousands of years. Muhammad's own father's name was Abdullah, or Abd-Allah, meaning "servant of god," and obviously he was named before his son was born.
I'm not trying to be mean or anything, but "allah" is not a word that belongs to Islam any more than "god" belongs to Christianity. Being offended by the use of the word "allah" in this case is the same as when Christians get offended by someone saying "Oh my god."