ChatGPT (probably other AI tools) has a problem in that it cannot reliably tell fact from fiction. It admits it if you ask it. So its responses aren't guaranteed to be accurate.
If the thin wire was part of an individual circuit then yes, that could be the culprit. If it was just one strand of a multi-strand heavy-current cable then no.
I have seen various posts saying that isolation/service valves sometimes weep after use. Are lever-operated shut-off valves for a domestic mains supply any less likely to weep/leak after use? Both types appear to be ball valves, which presumably have similar seals.
I share your concern about the naming of those zones. When some DIYer decides to hang a mirror/picture/cupbord by drilling into what they've heard is a 'safe' zone ........
Why couldn't they have been named 'wiring zones' ?
You could do the job with the circular saw, working with a straight-edge guide clamped relative to the board being cut.
But first make sure there are no hidden bits of nails/screws/tacks in the wood.
If you actually needed/wanted to tuck carpet edges under something you could just fix 1x1 battens at the edges of the area to be carpeted.
Unless the loft is frequently accessed, a carpet could be simply loose laid with no fixings.