You had loose bolts in your oil pan?!?!?!?!

Magnets are magnets and yes, they will pick up things that are metal (including most bolts). I'm not suggesting that it's snake oil because they use fake magnets or anything. I think if you drained your oil without using a magnetic plug, then ran a magnet through all the oil you just drained, that you'd pick up the same amount of filings as you would had you used the magnetic drain plug.

Doesn't the VW 944 have a [mostly] aluminum block?