There's a handful of questions about LEGO video games on Gaming SE right now. If I have a question about a video game, do I continue asking there since video games are quite different from the physical building sets themselves, or will they be on topic here as well?
I think if the question is primarily about the LEGO nature of the game, then it should be here. For example "What set contains the Joker figure #3 seen in LEGO Batman?" But if it's primarily about the game nature of the game, it should stay on Gaming.
I proposed a similar distinction for the LEGO boardgames on Area 51 - a question like "How can I build a Heroica-scale lava pit?" belongs here, but "How do I rebalance Heroica to make the barbarian's ability less useless?" goes to Board & Card Game SE.
My rationale is what the communities are interested in and know about - questions about LEGO come here, questions about gaming go there.