Nope, there's no line a ball has to cross or be inside of to be called an Infield Fly.
The rule book does define "the infield". The definition is the portion of the field in fair territory that is normally covered by the infielders.
On this play, it really does sound like the runners (or, their base coaches) are more to blame. If it
was called an Infield Fly, then they should have stayed close to their bases since they are no longer forced to run. If it wasn't, they should have stayed close to their bases until they were sure if the ball would be caught or not.
Here's a hypothetical question: How high does an Infield fly have to go before it's considered an Infield Fly?
The answer is, there really isn't any set height. A batted ball can be four different things: A bunt; A grounder; A line drive, or; A fly ball. And that's all we really have to choose from.
By rule, the first three can never be an Infield Fly. So, that kind of narrows it down! The rules define a line drive as a batted ball that travels parallel or near to the ground for most of it's flight. That really narrows it down! A fly ball is one that is airbourne and traveling a non-linear path, away from the ground.
If the ball has any arc to it, and it can be caught by an infielder with ordinary effort, it's best to call the Infield Fly. This protects the runners if the ball is dropped, as they are no longer forced to advance. The logical result should be one out, either on the Infield Fly call or the catch- poor baserunning by the runners not withstanding!