I love it when the STB gets feisty:
The Town and the Commission—of their own accord—set into motion the events that have necessitated the Board’s involvement while the state property litigation remains ongoing.
tl;dr: By not waiting for the MA court decision and instead trying to take the land by eminent domain, the town essentially forced the STB to be involved. STB decided that holding the docket in abeyance would cause irreparable harm to G&U, so it was compelled to rule and has ruled that the G&U plans to use the land for rail and rail-related activities, and therefore, the town is preempted from restricting that use or taking the land.