Is Moment of Silence supposed to work off structures?

Co-op Missions Discussion
1

When a Heroic enemy dies, all player units around it will reflect on their transgressions, leaving them temporarily unable to attack or use abilities.

So it triggers when you destroy a train (from OE), but it doesn’t when you take out a RtK void shard.
It doesn’t specify units, although it seems to imply that?

2

Far as I know Trains are considered units, as the very first mutation mission (if I’m not mistaken) was Train of the Dead, whereas infested units spawn on the train upon death.