That is certainly a lot more particles that you'd expect to find in an oil change.
Try to figure out what material the particles are made of - plastic, rubber, non-metalic metal. Hard plastic bits are usually from the timing chain tensioners/ramps. Rubbery yellow/brown bits are usually left over engine sealant and are normal and not a worry. Any metal bits should be investigated.
Post up pic's of the oil filer.
One of the problems is that its probably impossible to know when the last oil change was done. I would not rely on what the previous owner said unless he also provided a receipt. He wouldn't be the first used car seller to say that the oil was "just changed last month" when it was really two years and 15,000 miles ago.
If you have the time, you could drop the sump and see what's in there but if you don't have the time or inclination (and assuming the oil filer looks ok), I'd change the oil and drive it for a few months and then change the oil again to see if these results repeat.