Correct. The Wire is only in Z1 and Y3.
Since you can't drive on the top of a wall or half your wheels on a cliff edge.......................................Wire bog makes no sense in these cases despite lack of clarification in the rules. I'll just house rule this one.
ASL models many, many different effects that can combine in untold combinations, and IMO it does a very good job at that. Yet there'll always be corner cases where logic appears to break down, and which could only be solved by endlessly expanding verbiage.
You could house rule these cases when you spot them, which is fine if both players agree, but it's a slippery slope. The other alternative, though, is to shrug and say, "Hey, that's what the rules say. We both realize this seems a little wonky, but the rule is clear and playable, so we'll go with it as written."
And maybe it's possible that the wire-layers saw past the stone wall too, and even spotted some gaps in the wall, and--not being constrained by hex gridlines--merely extended the wire all the way to the house, "just to be safe". (Or maybe, when the lieutenant wasn't looking, they just tossed the leftover wire over the wall and left it lying there, unseen in the tall grass where, coincidentally, it might tangle in any passing treads.)