From Longman Dictionary of Contemporary Englishbe (quite) a different matterbe (quite) a different matter (also be (quite) another matter) especially British EnglishSERIOUS SITUATION used to say that a situation or action is very different from the one you have just mentioned, and may not be as easy, pleasant etc She didn’t mind seeing him in a group but an intimate dinner in a restaurant was another matter altogether. → matter
Examples from the Corpus
be (quite) a different matter• However, in the workplace, where productivity thrives on positive relationships, it can be a different matter.• But the possessions of the church of Canterbury were a different matter.• But the saying and the doing are different matters and are often worlds apart.• The others looked at me oddly; they didn't have bulimics in their group - that was a different matter.• But the Friday round, during which a steady rain fell unceasingly, was a different matter. 