Google the phrase a number of documents and travel blogs come up suggesting it’s a real thing. Also this reddit thread which you can translate from portuguese to learn the hiatory of why

This might just be a case of english speaking wiki writiers being lazy when it comes to foreign place articles.

“Because during the ‘Liberal Wars’ it suffered several sieges and was never taken, and it ended up being a very important starting point for the victory of Dom Pedro IV, who intended to secure the throne for Queen Maria II, who later bestowed the title of ‘Ancient, very noble, always loyal, and Invicta (Unvanquished)’ upon the city of Porto.”