unexpected spark

I was changing the spark plugs in the back are of my 91 grand voyager 6cyl and as i was trying to get to the back row facing the passenger side by alternator there was a quick spark of some type there..i disconnected battery finished plugs and restarted it.
didnt notice anything different.
what could that had been ?,possibly a short there at wiring harness to alternator ?.I didnt see any other wires that were directly powered unless car is running .I also saw a ground strap with a braided cordlike material there also.
Any ideas ?
thanks

One lead on the alternator is a hot battery feed. If you touch that lead to ground with anything conductive like a ratchet, it will spark.

thanks
i didnt have a tool around it i was just reaching back to pull the plug wire out..
maybe i pushed it against the metal of the engine support/etc .

did that harm anything as to the alternator ?

Alternator harmed? Probably not. You can check charge output from the alternator at the battery. Should see 13.5+ dc volts with the engine running. If anything it would more likely damage your PCM (engine computer) but if it's running fine with no check engine light then no worries.