Is this damp returning or something else?

I've recently moved into this property, this back room is 2/3rds submerged into the garden at the back of the house (house is built into a slope) and previously has had issues with damp that was treated in Nov 23 (not 100% sure what was done, I know the walls and floors were stripped, treated and then re-plastered and an extractor fan put in). I have noticed these discolourations/texture at the corners of the skirting boards touching this wall (the wall is absolutely fine - and the wall & skirting in an adjacent room that was also treated is all fine). It's not wet to the touch per se, but it is colder than the surrounding would and does rub off almost like putty. The patches haven't got any bigger over the month I've been here, but I'd like to know if this looks like just grime/filth or a return of the damp.

I hold a guarantee for the work from the contractor, I'm not confident to know whether to send them an email if this is easily provable to not be a problem and I should just clean and re-paint.

Thanks in advance!