Looks like it was a false alarm. I spoke to Royal Caribbean on X (was hoping to add my BAEC number to an existing cruise booking) and they came back with this:
Thanks for your patience. Between Friday 17th and Wednesday 22nd May we emailed new invoices for a number of trade and direct bookings across our International markets. In error, the invoice included some text which referred to guests collecting membership points with Avios.
Avios is the loyalty currency of the British Airways Executive Club and their partners. Currently, we don’t have the ability to capture Avios membership numbers, nor do we have a partnership with Avios. We have reissued invoices, without the text, to all impacted bookings and the message should be ignored. I apologise for any confusion.