Optic remebered that they are world champions.
The most reasonable argument you could make is that Masters is an INTERNATIONAL championship. If you win a masters you can call yourself a world champion because you've played against every top team from every region in the world and won. So yes, if you win a master you can call your team the best team in the world and a world champion.
IEM Dallas is IEM Dallas, MSI is MSI. Masters is masters.
If Masters wasn't a world championship then it would be just an useless international championship, a thing that is not... Masters is a world championship, if one day a Brazilian team wins a masters they will be a world champion, it's simple as that.