There are a lot of spassumptions on this thread that the caterers aren't able to run their business or aren't able to say, "sorry, no" to requests for a discount.
You are regular customers, and they didn't say no to discount.
What's the hand wringing all about?
Obviously they won't go bust because they have repeat custom and they've rewarded you as their customer by saying yes to a request for a discount.
I always ask for a discount, sometimes I get one, sometimes I don't, but if I'm a regular customer, I'm usually offered one, and am happy to accept. I always ask if I pay in cash how much is that? I usually get 5% knocked off. I hardly ever pay full price for things and have no problem giving discounts or contras to regular customers.
They will say no if they can't afford it.
No need to think your DH did anything wrong. In fact he sounds like he's very sensible.
Lols at the 'how would you like if you're wages were cut' comment: obviously that poster has no idea how restaurants, or business are run. The person working there isn't taking a cut in wages because of getting repeat business and keeping customers happy.
Business go tits up because they lose customers and can't get any more.
They can say no if they can't bear the cost, and to assume they're not able to run their business because of nasty clients asking for discounts is ridiculous and a bit white mans' burden TBH.
Enough of the hand wringing. You got a discount, so what? They're still making a profit, you're a repeat and loyal customer. You're happy, they're happy.
Bon appetit.