The recollections I'd had of Grant and Shula was that there was friction between the two--especially the shenanigans Shula pulled when he was chair of the Competition Committee and adjusted rules to neutralize some of the tactics and innovations that Bud's teams employed on the field. It's nice to read the article above and know that they were competitors but on good terms for the most part.
(I'm not sure exactly how it works, but Bud's tweets are restricted, and I think you have to follow him to view them including the top one in this post.)