Yeah, it seems that naming convention: “GraphQL Variable” is a relic for sure. I would think a more appropriate name would be something like “DQL Parameterized Variables”.
I checked out the parser for this in the code and it seems the only supported values for the array signature are UIDs. Here’s a GH issue to track: DQL variables don't seem to be supported in arrays · Issue #2272 · dgraph-io/dgraph · GitHub