[Arran]

I don't think it is really a concern, there may have been a small spark because whilst the neutral side of the household wiring is at zero, with respect to the two hot lines, it still may be above where an outside ground is, or even vice versa, so there may be a potential there rather then an electrical fault. This is also why I wince at people adding a grounded cable to an old radio with a grounded plug, the ground line runs all through the house and could be picking up electrical hash from anywhere. I've tried connected the ground terminal on an old radio to the power line ground but the results are mixed, sometimes it helps, often it does nothing but make the gain drop. On some sets you have to add am external ground because the volume control is in the antenna circuit and it won't work properly without it.
Regards
Arran