[happytoexplain]

This is a fine rule, but don't rely on it if you're trying to learn English. Typically, you simply wouldn't use the term "next <dayofweek>" in the first place unless context already makes it clear. E.g. you would only say "next Friday" if:

- Today (or perhaps tomorrow) is Friday, and so is clearly not the one you mean

- You were just talking about the upcoming Friday ("Not this Friday, but next Friday")

Also note that people often say "The Friday after next", referring to the Friday after the upcoming Friday, which breaks the "next" rule.