What are these black spots?

[Christian Nachtrieb]

Can anyone help me to identify these black spots? These are located on the backside of the (very) old baseboards on the plaster walls of an older condo. Wife is convinced this is mold, I'm not so sure. This location here is in one of the bedrooms, nowhere near the kitchen or bathroom, so I don't see any immediate ways in which water could've settled up here. You can find these black spots in a couple other rooms like living room and another bedroom. It looks charred to me?

Any idea what this could be?? We're having a mold person come and look at it, but I'm weary that he's just going to say YUP that's mold, hire me to remediate it.

Thanks BP!