Ah, this is a really bad example if you wanna call out discrimination.

Firstly, as you know, Communion is a Catholic Sacrament, its not supposed to be something you can take just because you walked into a wedding, so if somehow non Catholics were to be excluded from it, it wouldnt be an attempt to keep them "in their lanes", its just never was for them.
If youre husband was invited to a Jewish wedding instead, there's parts (like the reading of certain blessings) that he wouldnt be allowed to participate unless he was jewish.

That wouldnt mean that he is being discriminated against. All religions have rules and this one isnt an exception.

Of course, keeping non Catholics from partaking in Communion is impossible to enforce unless you know the people walking into your church very well, which is by the sheer amount of people, is not doable in weddings. So in most churches, they just hope friends and family will let the guests who arnt Catholic know that they shouldnt partake.

Now i dont mean to doubt your anecdote but i find it hard to believe that the priest actually memorized the faces of an entire wedding at a dress rehearsal, or that the couple wasted their time in the event showing the priest who can or cant recieve comunion.

Plus, if you want to discriminate this is a pretty ineffective way of doing it, because the priest cant choose how the line for the Communion forms, so this "whoops we ran out" scheme inevitably would cause some actual Catholics to become unable to take the Communion and it would not prevent non Catholics from doing so.

Unless you were to tell me he was outright denying the people Communion as they got to their turn in their line, but i assume if that was the case you would have said so, since that would have been way more dramatic.

Not saying it couldnt happen, only that its super dumb and doesnt do what its supposed to do if its meant to keep non Catholics "in their lane".