I've seen the site. The guy doesn't know BMW K bikes. With 80-85 psi oil pressures when hot and very high volume, particularly on pre-1990 Ks that were geared to spin the oil and coolant pump faster than on later bikes, bypass pressures are a real consideration when buying an oil filter. Many car filters will bypass at the normal oil pressures that K bikes run.
That high pressure and volume are a large part of what make Ks so durable. Now you want to throw it away with a car filter that might not be up to the K bike's oil pressure? It's your bike, but don't say I didn't warn you.