That is the appeal to Moomins in the sense of People of the Book and perhaps in a wider sense to all who are feeling divine Unity in their hearts.
Here’s an illustration of Muslim / Moomin:
A church may be marrying a different couple each day. Each couple’s ceremony is solemn and the biggest day ever.
The marrage itself is submission to law e.g. civil law plus divine law.
Islam = the marriage ceremony, with all its legal trappngs plus of course the couple.
Moomin = the faithful, the faithfulness of the couple
But also: Muslim = the marriage of the previous day in its own right [= past iterations of the faith e.g. Judaism, Christianity, Sabianism, or some other forgotten prophet]
And also: Moomin = in the deepest most specific sense, God pointing the finger at man and wife separately, and judging them to be faithful, knowing what noboidy else could really know for sure, whether they cheated or not, whether they even cheated with their eyes and thoughts (sure we can look and thnk about other people, but God knows the extent and only God can judge, though as an asides thoughts aren’t punishable but my point is, true Moomin = something only God decides)
Also Moomin = all true lovers everywhere, even those that never heard of the church hall where the weddngs are occurring but would surely get married there if they knew.
So you see, multiple sense of Muslim / Moomin but they are very much interchangeable and very much apprioriate to the same person at times, and to non-Muslim at times and to non-Muslims AND Muslims together, at times,