So my dads 2008 520d failed as they couldn't test emissions due to too much oil.

So I drained about a litre off to get to the MAX level.

After getting a call from my friend just as I finished I said what I was at and he mentioned about the DPF could be clogging up and they puts pressure into the oil system which would make the oil level seem high. Is this true?

Any way to test this out?

My dad's friend owns an SIMI garage and is trusted in the ability to fill oil. Very unlike him in his eyes.