ᐅ New construction mold on wall before final inspection

Hello everyone,
my construction project is progressing well. The screed has been in place for almost 2 weeks.
Yesterday I noticed that on one wall (southwest side)

there are 4 spots, each about 30cm (12 inches) long. The middle area looks particularly bad. I am attaching two pictures of it.
For your information: after the interior plaster was applied, it was difficult to air out properly. The exterior plaster was done during the same week. Therefore, the builder sealed the window with plastic sheeting. At that time, I was only able to tilt the window and make a small hole in the plastic.
Since the screed was finished (about 12 days ago), I have been actively ventilating at least twice a day for about 10 minutes each time with cross-ventilation. According to the hygrometer, the humidity is now around 55% on the ground floor and about 80% on the upper floor.

I think the mold was directly on the concrete (picture 3).

What do you think about this? Does this happen to you as well?
THANK YOU for your reply.