The chances of that actually happening are near impossible, and the lack of it happening doesn't mean equality of opportunity wasn't achieved at all.
Take for example a coin toss. Heads and tails both have an equal opportunity to win, there can be no arguing about not achieving equality there. Flip that coin 100 times and will heads and tails have won an equal amount of times? There's a chance of it, but it's far from a sure thing despite the equal opportunity.
Now add in a huge number of additional factors as there would be for a something like political positions as you mentioned and even if perfectly equal opportunity is still there, the chances of actually achieving an equal outcome are now much lower than it was for the coin toss.
Of course, this is all about probabilities. When I flip a coin 100 times, It's obviously unlikely that It's exactly 50 times head and 50 times tail but it's even much more unlikely that i get 100 times head.
Let's pretend for a moment that the chances of a parliament member being male or female is exactly 50/50. In Germany more than 50% of the parliament members are male (~70% in reality) but that's not a big deal because there's a roughly 50% chance that the majority of the members are male, so this could be just a coincident, maybe there's another country where the majority of parliament members is female. If we look at the 28 EU member states + USA and Canada we see that there isn't a single country with more female parliament members than male ones, the chance for this scenario to happen is 0,00000009%. With such a low probability I don't think it's a coincident so what we pretended in the first place must be false.
To your second point, what are these "additional factors" and are you sure these aren't contradicting the pretended equality of opportunity?
In practice, a 50/50 split is impractical because of your point and full equality of opportunity is not achievable, however a +/- 10% fluctuation should be feasible.
Well in regards to political positions additional factors would be political affiliation, I'm not sure what parties you have in Germany, but even if the number of candidates from each gender/ethnic group was representative of the population as a whole (and thus effectively equal), there's little chance that they'd be evenly spread across all the political parties. And not only does the party one represent play a role in getting elected, but each candidates personal ideas would also play a role. I guess you could argue that means there's no equality of opportunity, but that isn't necessarily true.
Additionally there is the fact that politicians are typically elected on a regional basis. So like the party affiliations, you'd also need an equal spread across all regions, and again not having so does not necessarily mean there wasn't equal opportunity.
Although really political positions are probably the hardest thing to actually have an equal outcome on despite how equal opportunity is. It doesn't really take ability into account, so unlike other professions where you'd expect equal ability (whether gained through natural talent, education, experience or any other method) to result in equal success, that's just not how politics works.