I don't think honoring the religious traditions of other people is cultural appropriation, but there are ways to do it sensitively and ways to do it clumsily. In general, various religions invite others as a gesture of hospitality. I'm not Jewish but I've been invited to probably 20+ seders in my life, mostly in the homes of Jewish friends. I'm respectful of the traditions, and say whatever prayers are required for the occasion. In various parts of the country, Catholic parishes offer some sort of fish fry on Fridays during Lent, and people who come don't have to show their "catholic card". But in general, Catholicism doesn't have many rituals around food and food preparation, which both Judaism and Islam have in spades. Some Catholic countries have special meals before Christmas (the meal of the 12 fishes, or the meal of the seven fishes for instance) - but that is not universal by any means. Both Judaism and Islam have many precepts about sheltering strangers. (A remnant from their tribal origins, when nomadic people depended on a kind reception at an oasis or well). I'm sure that if Greg's parish has made overtures to the Muslim community, informed some community Muslims of their desire to hold an Iftar and seeking advice on how to do it in the most respectful way, it would be looked upon very favorably, particularly if they invited representatives from that community to assist in the preparation and participation in the eating of the meal, maybe a presentation about the history of the tradition, as well as ecumenical prayers.
There's nothing grosser than people inviting people of other faiths and then lecturing them or offering prayers for their conversion to the faith of their hosts.
Along those lines, there's a very old Jewish joke about a lone Jewish man living in a small village in medieval France. He was very well-liked as the best tailor around. . However. on Friday afternoons, when the village people were preparing their dried and salted cod meals or some barely edible lentils and bread, they were tortured by the delicious smell of chicken soup wafting through the town as the tailor prepared his sabbath meal. Finally the village people couldn't stand it. They went to the priest and said, "Father, you've got to do something about Moishe. He's driving us crazy on Fridays". After a few weeks, the priest decided he had no choice but to forcibly convert the tailor. So one day, the townspeople burst into Moishe's home and dragged him off to the church, where the priest did a formal conversion ceremony, culminating in the words, "Domine domini domini, once a Jew, now a Christian". Everyone went back about his business, relieved that the matter had been settled and they'd no longer be tortured on Friday afternoons. However, the next Friday arrived and once again, the delicious smell of chicken soup cooking wafted through town. Now the townspeople were livid and en masse, they sped to Moishe's house, determined to punish him. When they burst through the door, there was Moishe in front of the fire where his soup was cooking. He was on his knees, desperately saying a prayer...."Domini domini domini, once a chicken, now a fish".
PS Catholics do "real fasting" on Ash Wednesday and again on Good Friday, where food is usually not consumed until dinner time. (The "rule" is only one meal eaten on that day).