This type of occurrence is called a split due to a weak crotch and two competing leaders. The split has been inevitable for many years, and was just waiting for the weight of wood on one side or the other to pull the branch down. It is quite commonly seen. The activity in the root zone probably has no relevance; while this may have reduced the overall vigour of the tree the split was an event waiting to happen for many years.
Tree surgeons are often able to detect this kind of weak crotch and can either reduce the weight of wood on the weak side or brace or cable the two competing leaders together, each supporting the other. Ideally when a tree is young and it is clear that two competing leaders are developing we can remove one so that the weak crotch never develops and the tree can fill in the inevitable gap. However, interfering with the point of weakness to detect its state of rot itself would probably weaken it further so the operation would not be carried out.
Local authorities are usually very careful to lay cable only on land they own. If private tree roots expand onto their land then that is unfortunate but they can have no responsibility for damage caused to the roots.
Most trees, including Liquidambar, are subject to the competing leader problem. When inspecting trees, look for the angle between the competing stems; a wide angle is perhaps okay, but a sharp or acute angle is a sign that weakness may be present.
Edit: when you come to do the cleanup, examine carefully what remains of the tree once the fallen part has been removed. You may find that the remaining leader is badly unbalanced and might need to be reshaped to restore some stability. Assess where it might fall if it goes over and evaluate potential damage if and when it does.
