Why are you called a Jew? How do you know you are from the tribe of Judah? You are at least as likely to from Levi, Benjamin, or stragglers from the other tribe. Based on DNA, most of your ancestry is probably from converts (at least on the female side). However we use the term Jews.
We call millions of people “Indians” even though they have no connection to India.
It’s been a convention for millenia to refer to the Arabs as “Yismaelim”. While their is probably a connection for the Arabs who live near Eretz Yisrael, most are descended from whomever was living there when the Arabs conquered them (e.g. Iraqis are descended from Babylonians, Palestinians are descended from Hellinized Jews, Greeks and Romans- and of course the Egyptians are descended from the ancient Egyptians though the “white” Egyptians who run the country are largely of Arab descent).