Yes, Mahou San Miguel owned 30% of Founders. The craft brewery threshold is 25%. That Mahou investment was made 5 years ago and at the time there was a provision for them to buy out the company at the end of five years so apparently they were satisfied enough with their investment to do just that. The two owners each kept 5%.
As far as I can tell Mahou has never interfered with the brewing at Founders. They have provided the capital for growth but have left the beer making decisions to people who are on the front lines at the brewery. That system has seemed to work very well with Founders building a new brew-pub in Detroit, a new production facility near Grand Rapids, contract brewers in other states to expand distribution. Since the 30% buyout five years ago they have gone from state wide distribution to regional distribution and now to national distribution.