This is probably a terrible comparison for a European, but it's like firing a gun in a room vs. firing one outside at a busy rock quarry. Duh you're going to hear it in the room, but it might just blend into the background noise of an outdoor noisy area.
Your little plant in your room has a dominating aroma because it has such a small space to fill and not a lot of competition with other smells. Outside the little plant would not only be competing with all the other odors the world has to offer, but it would be getting whisked away by the breeze and dissipating over a very large area.
The secret to a good balcony grow is finding a couple of strains that don't reek to high heaven, or some that just don't smell like pot. BOG's Bogglegum is a great beginner's strain that has almost no odor. You could grow one of those on your porch without much trouble.
