It obviously does discriminate against people by marital status, because if you're not married, you're not liable to be rejected based on the spouse-dinner filter.
It's a little like suggesting that you're not filtering based on religion if you ban yarmulkes.
I'd say its closer to finding out the single guy is in a gang and since he spends time with crazy people you don't want him. But I guess your point is at least a bit valid. That being said, it seems only a few states have a problem with using married status in hiring.
It's a little like suggesting that you're not filtering based on religion if you ban yarmulkes.