Agree, looks like the vias were exposed to wave soldering, but had goo retained or trapped inside the barrel. Goo might be soldering flux, contaminants, moisture*, etc.
*Seems unlikely though, vias should seal pretty well. Do they usually have porosity that allows moisture through (from the core/PCB/laminate)? Or is it more a matter of, the PCB material was just that humid, and it had to come out somewhere?
There could also be goo trapped from a previous operation (via plugging, or trapped flux that wasn't cleaned -- or no-clean was used(!)) that bubbled on a subsequent operation. As amc184 is hinting at...
Tim