Dealing with guests of your guests

So, we have a strict "No date unless it's a significant other policy". As we all know, receptions get expensive and we've already cut plenty of costs for the wedding.

Though we explained this policy to our friends, one still RSVP'd with a guest. Mr. Chic 'n Cheap regretfully told guest that we could not accommodate guest's guest because we were trying to keep the wedding small.
Guest responded by telling us "You're so messed up."
We apologized and cited the tight financial situation.
Guest said "Maybe I won't come and save you guys money."
No word since...

What happened here? Guest was a good friend and we're kinda baffled by the response. How do you deal with guests that want to bring other uninvited guests?

We're going to wait and see. But it's a sad situation.