I often encounter people who assume that all Arabs are Muslims or seem to think that all Muslims are Arabs. Neither are true. There are Arab Christians and Arab Jews (and I’m sure there are Arabs who aren’t religious at all). Arab Muslims don’t even make up the majority of Muslims (the largest Muslim country is Indonesia, after all).
Here is a short article by Haoon Moghul pointing out the fallacy of such thinking: Why Arab and Muslim Are Not Synonymous.