-snip- As for the wallet already being there when I installed Electrum it makes me wonder what are the odds I would randomly select a wallet that just happened to already be on my computer?
There's a 90% chance that it'll be pre-selected.
Since it's in the data directory where the configuration file is included where the previously loaded wallets are listed,
chances that it'll be the very first wallet that a newly installed Electrum will show during its "
Install Wizard" screen.
Plus the data directory isn't deleted if the previous owner deleted/uninstalled Electrum.
Why? Is there a chance that the PC is someone else's?
Because that's a good start since you can ask him if he used Electrum before and the whereabouts of that address.