31a is not connected to the line.
There are four characters. Two of them are connected to the line - but 'connected' does not mean they touch the line - they are connected in a different sense to the line. One of them, coincidentally, forms part of the line in the grid (but the instructions do not require it); the other has escaped.
The other pair of characters has no connection to the line whatsoever, though one of them is the builder of what's represented by the whole grid.