Yeah, I remember this. Even in Musters prime (1995-96) and at a time when Edberg was far over the hill, Edberg still beat Muster 5 times out of 5. Impressive.
Yes, it was just a horrible match up for Muster and unlike Sergi who could hit chip returns at the feet if Edberg wanted to volley, that was something Muster couldn't do effectively.
Plus Muster stood a fair way behind the baseline and Edberg was comfortable with his movement on clay and gave him enough time to get into the net and put him under pressure.