This summary is not the rule. The rule text controls.
If you file a motion in your case, it's your job to actually get it in front of the judge and get a decision. Filing the paperwork isn't enough. You need to follow through and schedule a hearing so the court can rule on it.
This includes motions for a new trial, not just regular pretrial motions. If you file a motion before trial but never get a hearing on it before the trial starts, the court will treat it as if you gave up on that motion. In other words, sitting on a motion and not pushing it forward counts as dropping it.
That said, the rule gives judges some flexibility. Even if you didn't get a hearing before trial started, the judge can still choose to hear the motion after the trial has begun. This isn't guaranteed, though. It's up to the judge's discretion, so the safest move is always to request a hearing and get your motion decided before trial starts.