Oats are definitely one of the five grains.You misspeak.
“and most importantly, they do not naturally contain gluten.”
You like many others, have a slight bit of misinformation. The jury is still out on this one. Many specialists believe that oats can contain gluten, and not all of them agree that it is safe for someone who has celiac to eat oat-based foods. It is possible that SMALL amounts of oats may be permissible. Or, it is possible that a certain TYPE of oats or oat product may be safe to eat in small quantity. Buit it is not a blanket statement. And it is always preferable to see a “gluten free” label on the item, to be sure.