That's always been my understanding and I worked in/around beer/beverage during the time that Cinco de Mayo first came to be celebrated.
My recollection was that Anheuser-Busch first started it, the ploy got picked up by the rest of the brewers almost instantly....that business is so incestuous it's silly at times....then someone decided to enlarge the pull tabs so the customer could REALLY chug 'er down and all the engineers/production staffers got to rack up two or three MORE weeks of unpaid overtime to make it all happen.
(I still wonder why I stuck with that stuff as long as I did....40 hour paycheck for 75 hours work and every now and then hear the boss say "We'll make it up to you...".)