My understanding of what he was saying was that there was no second grid wire connected. Once he connected it, the LV2424 was able to correctly sync to split phase.
When you have grid in, it syncs to the grid. When you don't it produces its own phases. So, it can't sync to split phase if you only have single phase coming in.
From everything we've seen so far, the LV2424 is very smart and does a great job of syncing to grid input and, as we learned from Mac, does a decent job handling human error in configuration. This is also good to know because, in theory, there are other reasons this could happen, such as one of the grid inputs later becoming disconnected (e.g., mouse chewed it?)