I feel sorry for you. something similar happened to me recently as well. They also insisted on a breath test that was completely irrelevant. An insulting presumption of guilt.
They're allowed to do random tests.
Especially if they see someone do something which stands out that they might not be fully in control of their faculties.
Going down a one-way street the wrong way would give them cause no doubt, or a few swerves down the road, etc. Maybe totally innocent and accidental, but there's always that chance that they could be drunk or stoned.
And I reckon it's a great thing; I'd hate to be a parent who gets the knock on the door one day to say their child was killed by a drunk or stoned driver.. I personally know of one guy here in our little town who has lost his licence for .05, and yet still drives to work, and still gets very *****ed a lot of nights, so would probably be over the limit the next morning when he heads off to work early (he's a tradie). Don't worry; I've done my civic duty and informed the local cops.
I much prefer to see cops out and about catching offenders than speed cameras, because the cops can use their (hopefully; good) judgement in every individual case, and catch drunks and druggies at the same time which a camera could not.
Not only that; a more visible police presence is a very good deterrent against all types of traffic offenses and crimes;
For example; everyone slows down for speed cameras, but as soon as they are 100 metres past it, they speed up again....but if you are driving down the road being followed by a cop, you will sit on the speed limit for as long as they are still behind you. Seen it happen a million times in both cases...human nature.
But plenty of drivers get let off with warnings when they get a cop in a good mood and the driver is polite to them.
Not saying the original poster wasn't polite; just unlucky.
But we don't know the circumstances either; maybe there has been a lot of these incidents, and someone complained, so the cops started to do some regular surveillance on the spot?
For example; slightly different but similar; we have a laneway directly behind our workshop, which services building deliveries on both sides. We use it to access our back hoist for car repairs etc, and we need our entrance clear so we can get cars in and out. The delivery vans stick to one side or the other to allow through traffic, and every so often will park in front of our entrance, but this is no prob as they are usually gone after a few minutes.
On our side of the lane there are "No Standing" signs with arrows pointing in both directions, spaced around 25 metres apart, on the other side there are right angle parking spaces. It is very obvious that you cannot park on our side of the lane.
In recent months, there have been an increasing number of people parking in the no-standing areas, and sometimes all day; blocking through traffic if there is a delivery truck stopped in just the wrong spot. It annoys me because it affects me with longer hold-ups for the deliveries or people stuck waiting directly in front of our driveway - we can't get in or out, and sometimes customers are waiting for their car..
It all came to a head not long ago when there was nearly a punch-up between a delivery driver and an impatient car driver trying to get through the laneway - all because some @-hole parked in the no-standing zone, and had been there most of the day.
So, I complained to the Council, explained the situation, and now; they have random Ranger patrols of the lane and have fined a good number of these selfish pr!cks.
This maybe the sort of thing that has happened with the original poster.
Incidentally; I reckon the cops would view going down a one-way street the wrong way similar to going through a red light? - potentially as dangerous.
In any case; he entered the one-way street the wrong way, and was illegally parked (facing the opposite direction to street traffic), so not much of a leg to stand on with that one I'm afraid.