Nixon was being investigated under a criminal proceeding, which was the basis for subpoenas, which he defied, which was the basis for the article of impeachment against him. Anything else is just you attempting to redefine my argument and demanding I defend your interpretation.
You're now saying one thing lead to the other. Before you were saying one thing was the same as the other, which is not true.
The Nixon impeachment was based upon the criminal Watergate incident, so yes, it was a criminal proceeding.
An impeachment isn't a criminal proceeding. I think you at least understand this now.