I have this question too!
I think he means “filled vias” which means there is solder all the way through the via, which makes it able to carry more current with less heat. Look at the description of “conductive filled vias” at the bottom of this link:
pcbuniverse.com/pcbu-tech-tips.php?a=5
Right now I have some vias that are 125 mil in size, to be able to carry as much current as .100" traces (up to 8A) without overheating. If I could get conductive (solder) filled vias, a 50-60 mil via would be sufficient.