Perhaps what will help is to understand how our brains actually work. When we experience things, our brain takes in a lot more than we realize, this means that if someone walks down a busy street, there will be a lot of different things in that environment that our brain will take in. Our brain is receiving messages from "all" our senses in that experience which includes sights, and sounds and smells too. The brain stores all these experiences in different areas of the brain too. We may not remember some of these things but often we can remember "for example" smelling the smell of fresh bread being baked. Then at some point later when we smell that smell, we will think, hmm, I have smelled this before and that can lead to remembering how when you walked down that busy street you passed a bakery. In a way this can serve as a locator too, where you might sit and say to yourself "I want to buy some fresh bread", then as if in a miracle your brain remembers you actually know this because you remember smelling bread baking when you were walking down that street and then you end up saying to yourself, "ah ha, I know where I can buy some fresh bread".

The same is true when a person experiences a trauma, the brain records a lot more about our environment in that experience than we realize, and that includes smells, and sounds. However, this time we remember these things because our experience was bad or traumatic in some way. Well, this is a kind location ability we have as well, this doesn't mean it's bad either, all it means is that our brain will also let us know we may be near something dangerous.

So, to answer your question, YES, a person can be triggered by sounds and smells that may be connected to a trauma environment, yet keep in mind sounds and smells are reminders for a reason and they are not always for bad reasons.