This is a very common model.
What these websites do is scrape the Internet looking for coupons. If they notice that your coupon is attracting traffic they will look for a affiliate program and look to make a commission from sales.
Nothing wrong with it in my opinion, I am biast myself as I own such a website (although I do everything manually including 100% unique content). But some large companies do not like coupon websites as it can be abused.
So it's nothing to worry about, it can also create a good vibe around your business.