I suspect he dropped the plug into the funnel and, er, plugged it.
The only time I ever made a mess was getting the oil from the tray into the bottle, that bit where you think "well, phew the hard bit's over with no accidents, the rest is down... er, down my sleeve
Is the Citroen worth much? on paper I guess it would be £3K I dunno it would just be a shame to see it eat itself for the sake of a £40.00 oil change every 6 months, and it's our main transportation solution at the moment so all kinds of sh*t will ensue if it was off the road.
So it's worth the effort, but I wouldn't worry too much (well, I would, but I worry about everything) as you're doing your level best (well, you could change the oil every 1,000 miles but that would be mad) so if it does go tits-up it won't be because of something you did (even if your mrs insists it is)