Yes, this is correct and applies to all Catholic records, not just the Netherlands.
There is however an alternative (but extremely rare) system of grades that possibly could have been used called the Roman system. Under that system a 2nd grade relationship is a sibling, and a 4th is a cousin or grand nephew/niece. To be absolutely sure, check the other marriages in the marrige. If you see 2nd grade relationships, you know they must be using the official Catholic system as sibling marriages obviously would never have been allowed.
Recently I came a marriage where a 4th grade relationship was noted. This was in the 1750s in Hees, Gelderland- putting their common ancestor in the 1600s. I suspect they were noble/landed gentry, so they were more likely than the general population to know their ancestry.