And if a sojourner [ger] sojourns among you and would keep the Passover to YHWH, according to the statute of the Passover and according to its rule, so shall he do. You shall have one statute, both for the sojourner and for the native.
Numbers 9:14 #behaalotcha

The sojourner in Torah isn't a pagan or unbeliever. He is a worshiper of the true God of Abraham, but he is landless because he was not assigned an inheritance at the beginning or else has been dispossessed for some reason. But he is still Israel, none-the-less, whether native or grafted in. Passover is for all those who want to leave Egypt and be part of Israel.