Problem is, there is no rule defining when it is a swing. Most umpires just look to see if the head of the bat crosses the front of home plate as their criteria, but that's not the rule. Much like many things in baseball that we think of as "rules", most of them are simply umpire discretion. Like in the 2008 ALDS Sox vs the Angels, when the Angels tried to score the go ahead run via squeeze play and Varitek ran Reggie Willits back to third and tagged him amidst a fall/diveg, and then in the process dropped the ball. But the umpires ruled Willets out anyway. Why? Because there is no rule that says if the fielder drops the ball during a tag play that the runner is safe. And there is no rule that says the runner is out if the balls is dropped. Control of the baseball in this case is 100% umpire discretion.
The same goes with the nearly impossible call of check swings. All a swing is per the rule book is an attempt to offer at a pitch that is not a bunt. Did Flores offer at the pitch?
Not to mention these calls are made from 90-100 feet away by an umpire trying to judge the distance for a bat traveling some 75-80 mph for maybe a fifth of a second.
I've seen calls before I did not agree with. Heck, I did not agree Flores swung. But that doesn't mean they were bad calls that violated the rules of the game...