Second, does it imply anything? That could be answered by doing a survey asking something like this:
Which one(s) of the following would you expect to constitute seasoned ground beef if mentioned in an ad for a food item in a restaurant?
a) ground beef, chili powder, salt, pepper, cumin
b) ground beef, water, chili powder, salt, pepper, cumin
c) ground beef, water, oats, yeast, chili powder, salt, pepper, cumin
If you don't get a substantial number including (c) then you've got misleading advertising on your hands.
That statement is just plain false. Just because someone has a unique recipe, that doesn't mean they're being misleading. Instead, it just might mean that they're innovative, or that they have a patent, or that their just WEIRD... I mean, most recipes for taco seasoning doesn't have cinnamon in it. But I have a friend who uses cinnamon in hers. Does that mean she's being "deceptive" when she calls her seasoning mix "taco seasoning"? Of course it doesn't.
I believe there are some trained cooks here. I'm not one, but I cook and bake a lot. While I would add water to ground beef when making taco meat, I would not add any starches. If I did, it would probably be corn starch. What concerns me is that the combination of the oats, yeast, water and heat results in expansion. Personally, I've never added yeast to anything I didn't want to rise at least a wee bit (maybe that's my lack of training). To me that implies that Taco Bell is, in fact, using a "filler" to make it look like you're getting more ground beef than you really are.
I happen to be one of those classically trained chefs. Your assumption here is flawed.
1) Oats on their own do not rise just by adding yeast. You have to get oat FLOUR, add water at the right temperature, and yeast, and let it sit. Just mixing the raw ingredients without going through the right process won't yield any "rising". Thus, no filler action happening. Note, the ingredient listed is oats. Not oat flour. If one is using oat flour, generally one must specify that on an ingredient list. So, even more evidence that no filler action is happening in the manner you postulate.
2) Yeast is used for a heck of a lot more in cooking than just as leavening. It's also used as a flavor agent, not unlike MSG. To make the assumption that taco bell is attempting to add leavening to their taco meat, when the more simple explanation (given 1) is that they are, indeed, using it as said flavor agent.
3) Oats are used for many more things than making bread. They are used in a number of ways, as well as being a texturizer. In this case, that's how taco bell is using them.
4) You may not add any starches, but it is definitely common to do so, no matter what google tells you. Having spent time in industrial kitchens, I can tell you that you probably have NO idea what goes into the food you're served in a restaurant. Adding starches of various sorts to ground beef is par for the course, for any number of reasons. Flours/cornstarch/meals to get seasonings to stick during the cooking process, as a binder, as a thickener, to add texture...
Attempting to insinuate that there's something "deceptive" about a very
normal cooking technique, is just plain stupid in my opinion.
There's a case here. I can't say where it will go, but I doubt it will get tossed. I predict a settlement and a modification to their advertising once this dies down.
For anyone who knows anything about the food industry, no, there is no case here. No case at all. In fact, the entire idea is laughable beyond belief. But judges don't go to culinary school. So, instead of being hand-waved off as the inanity it is, this will probably end up going somewhere, and being messy, and stupid, and get blown totally out of proportion...