So the oil light was only on while the engine wasn't running? I can't imagine why that would be
The oil change itself wouldn't have anything to do with this. Not ruling out that something didn't happen during the process though, who knows what wire could've been tugged on, or sensor bumped, or... could be completely coincidental. Maybe they made a big mess and washed down the engine compartment with water and something got wet? I suppose that could be possible too.