To offer a slightly different perspective...I obviously don't believe that "Muslim" is a race, but to many white-supremacist and Islamophobic groups it may as well be.

Islamophobic prejudices don't get applied to White or Asian Muslims in the same way as for Muslims from the Middle East, because people seem to be assessing whether they look like the guys they saw on the news. I want to, for example, bring up the case of an Indian software engineer from Kansas who was killed two years ago:

The suspect in the shooting, Adam Purinton, was drinking at the bar in Olathe, Kansas, at about 7:15PM that night, the Kansas City Star reported. A witness said he yelled “get out of my country” to two of the victims, reportedly saying the men, believed to originally be from India, were “Middle Eastern.”

I'd also like to cite Wikipedia's article on Islamophobia, and the section about the relationship of Islamophobia and Racism:

Some scholars view Islamophobia and racism as partially overlapping phenomena. Diane Frost defines Islamophobia as anti-Muslim feeling and violence based on "race" or religion. Islamophobia may also target people who have Muslim names, or have a look that is associated with Muslims. According to Alan Johnson, Islamophobia sometimes can be nothing more than xenophobia or racism "wrapped in religious terms." Sociologists Yasmin Hussain and Paul Bagguley stated that racism and Islamophobia are "analytically distinct," but "empirically inter-related"

SO, the argument I'm putting forth here is this:

Muslim people do not constitute a race, but the people who are prejudiced against them (and those who physically attack them) often believe that they do. Using the word 'Muslim' as a weird synecdoche for 'Appears Middle Eastern' is common enough, and I believe that people who hate the nebulous group of 'Muslims' are holding racist beliefs against a race that they have misnamed, and largely imagine to exist.

In the case of Roseanna and Amy, I would guess that they have learned Ilhan Omar's name and may be vaguely aware of her nationality, but probably subconsciously conceptualize her religion as her race and act with according prejudice towards the congresswoman.

...Or that's how I think about it, anyway. Do you think I'm maybe not being fair? Honestly, there's a chance I'm assuming too much about Roseanna and Amy. Idk. The idea's out there, I'm curious what you think about it!