If you have a break scheduled after round 4, then during that break it is still technically round 4 (because round 5 has not yet started).
A possibly better way to put it is that during the break after round 4 ends, the tournament is currently in a break but the round number is still 4.
If you've got an event that fires at the start of round 4 but don't want it to fire at the start of a break that happens to be directly after round 4, you would set the trigger to "A level start" and set the conditions to:
isRound and (roundNum = 4)
Without the isRound part, it will fire at the start of round 4 AND at the start of a break that is immediately after round 4. isRound will be true during any round but false during a break. This prevents it from firing during the break after round 4.