Birds are a clade of dinosaurs ( a child group). In exactly the same way, dinosaurs are a clade of reptiles. So by extension, birds are a clade of reptiles.
I think they were pointing out the structural issue with your statement. They info you are attempting to convey is correct. Your ability to do so is questionable.
I'm not sure what is structurally wrong with that statement. Birds are dinosaurs (most people know this by now). Using the exact same logic, dinosaurs are reptiles as well.