Hello,
How close were your units to Sweden's cities, or units, and also what sort of units did you have trapped? I know that units will "jump" when they become so close to one another. It is also possible that they could have engaged you. Ranged units you would have to be careful of, and neither country would be able to pass through the other.
You can tell him that it was an accident, if you capture a province offer it back, or you would have to continue fighting.