I think I’d go with the Muslim school.
As you said, there’s no risk of confusing Islam and Roman Catholicism, or having the very real issues glossed over and your children leave thinking there’s much more in common than there really is. Plus, especially here in California, you’re more likely to get actual conservative teaching and culture at a Muslim school than a Roman Catholic, which in this state are rife with liberal positions.
However there is a much higher risk of pressure to convert from the other kids - it’s much easier to convert to Islam than Roman Catholicism. On the other hand your child is much less likely to accidentally receive a non-Orthodox Sacrament at a Muslim school. So long as you can assure your child is going to remain strong in their faith, and are able to put up with constant pressure to convert (which, really, is the same at a public or Roman Catholic school, it’s just ‘converting’ to secular humanism or to liberal Christianity) I’d say go with the Muslim school.
Would your kid be able to opt out of prayers or services? Are they going to have difficulty eating lunch during Ramadaan? I don’t know the rules about those types of things.
You might want to sign up and ask your question over at The Ancient Way forum, where you can get answers just from your Brothers and Sisters in The Faith. God Bless!