Is it wedding etiquette to invite the husband?

One of my childhood friends is getting married this November. Even though we grew up together, our relationship has pretty much been reduced to Facebook friends and we only check in on each other a few times a year. I received the rsvp invitation in the mail today and on it, she only put ‘one seat’ reserved.

I’ve been to about 10 weddings and this is the first one I have ever been to that my husband isn’t invited. I thought maybe there was an error so I messaged her asking if I could bring him and she said no because she doesn’t know him.

I can’t help but feel a little offended. This is weird, right?