...and that ain't no bull?

It's a big country, Granny with a great many sub-cultures who speak a large variety of sub-dialects of English. I can scarcely understand some of my younger city cousins when they're chattering amongst themselves. Their vocabulary seems comprised mostly of verbal shorthand, tho fortunately they're always willing to translate for me. I well remember myself as a young teen with my peers inventing words and phrases intended to mystify the adults around us. I think it gave us some sense of control over our lives which seemed to be dominated by adults.

The phrase you refer to however, has been in common usage throughout rural western North America for at least 50 years. I have heard it used by ranchers and bankers alike. And you must admit that it's a bit more colorful than: ". . . and I aver those to be the true facts." :-)

Television commercials, of course, target the audience the merchandiser has identified as being most likely to buy his sort of product. I'm not surprised therefore that the advertiser in question used a phrase lifted from the sub-dialect of a particular large class of consumers. Was the product a pick-up truck by any chance?

There doesn't appear to be a question here. Anyhow, "bull" is a shortened version of a word that would be even more indicative of the dumbing down of America.

Could it not be a pun if they are advertising meat? To imply it is tender beef.