The Rattlin’ Chug Bug doesn’t have a super deep cup to the mouth. Storm opted not to add a split ring to the line tie eye, something you’ll see on some topwaters. Storm likely opted out on the split ring to keep the nose of the bait up. It doesn’t seem like a split ring would weigh all that much, but it can often be enough to throw the whole balance of a bait like this off and cause the mouth to dig into the water too much.
You could try adding a split ring if you’d like, but it’s not really necessary. Simply tie this bait on as is and you’re good to go. If you’re wanting to walk the bait more though, it might be a good idea to tie it on using a loop knot. This will create a similar hinge to what you’d get out of a split ring, without adding any weight to the bait. But if you’re just wanting to pop the bait along, whatever you’re preferred knot is will do just fine.