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I have learned that what transpires between two people is none of my business unless I am asked by one of them to intervene/contribute.
The father of the LW was stepping out of bounds. Perhaps he doesn't like the boyfriend and didn't mind the opportunity to stick it to him. In any case, the issue was between the BF and the host. If the father had no intention of demanding the BF to pay him back and would not hold it against him for the rest of his life, then perhaps that would make it all right for him to 'contribute'. That would create another 'issue' between the father and the host only for no one else to butt into.
Perhaps the BF repeatedly said "No" to the offer of the money but the host insisted.