by DocCool
Swarmlings usually have lots of resources going into the last round, upgrading digging makes more sense for them than most factions, also late D expansion is usually part of their plan.
The former would imply that they are doing it for the VPs, while the latter would imply they are doing it to actually get more digging done. Which is why a "lackmus test" would be good, e.g. "how many digs did they actually do after advancing it twice?". If it's zero (or probably even once), then it was for VPs, if it's at least twice it was probably for the effect (and the VPs were a welcome addition).