The sentence: "yes, because we are actually stopping at them" is in reference to the subject: "the traffic lights". The originator of the sentence was intending to convey the meaning that Germans - in general - stop at the traffic lights, whereas non-Germans, generally, do not.
Ask yourself this question: Are they stopping at the traffic lights right now in the present-progessive sense? Is the speaker talking about doing this 'right now'?
Based on your link, use number 4 of the present progressive fits the OP's original statement: "actions happening around the moment of speaking (longer actions)"
In that case, the sentence would be properly formed thus:
"The Germans do stop at traffic lights. Non-Germans, do not."
Notice the difference?
Final Edit: the German-formed sentence I was correcting:
"Yes, because we (Germans) are actually stopping at them!"
.. becomes:
"Yes, because we (Germans) do actually stop at them."
Now, we can certainly look at the downvotes I've earned as a result of my personal foul use of language, but for the German-native speakers who make this mistake, it makes a huge difference in how well they are, actually, understood by English visitors. Please re-read, and see for yourself.
This is off-off-topic, but I wish forums allowed users to state that they would be happy to have their grammar and spelling corrected by ticking a checkbox, and that every comment could have a sub-discussion just for that, on its own page. That would be useful, or? (<-- joke :P) Because otherwise whatever you do, it's wrong: making a correction makes you seem like a jerk, and not making a correction makes you feel like a jerk (because you know something they don't, and you're not sharing it).
Also, your sentence
> Yes, because we actually stop at them!
> stop at them!
> at them!
Muphry's law: https://en.wikipedia.org/wiki/Muphry%27s_Law