Further confirmation can be found in the previous season of Strange New Worlds during the Lower Decks crossover, of all places. After Ensign Boimler and Ensign Mariner were thrown back in time 120 years, a throwaway line between them foreshadowed the latest episode in spectacular fashion.

You'd think the show itself would clarify who the mysterious bartender glimpsed in 'Wedding Bell Blues' actually is, but instead you'll have to read an interview to know for sure.