What's the etiquette for the host if they specified "no gifts" on the invite and someone brings one anyway?

We're hosting a birthday party for Xander in a few weeks and we specified on the invite that he didn't need any gifts. One of the RSVPs asked what he wanted, and I reiterated that he didn't need anything and we weren't expecting any gifts, but she just said "I'll ask (son's name) what Xander wants." So I'm pretty sure they are planning on bringing a gift anyway.

My plan is to just not open the gifts at the party since most people won't have brought gifts. And then just send a thank you note after to the gift-givers (actually, planning on sending a thank you note to everyone, but will include wording thanking gift-givers for their gift). Does that sound like the proper etiquette?