SHI: “Flemish” is Dutch. Flemish is just a name for a regional variation of the Dutch language in Flanders.
I do not agree. That’s Dutch politics and especially Dutch nationalism talking, not linguistic science. I believe that most linguists agree that Dutch and Flemish are two separate languages. And Ethnologue says that Flemish and Dutch are two different languages. Also I believe that mutual intelligibility is not good between Flemish and Dutch regional forms. Yes, Official Flemish is intelligible with Official Dutch, but those are artificial languages. The real true Flemish of regional lects has poor intelligibility with any form of Dutch. And Flemish speakers cannot understand many regional forms of Dutch.
Hell, Dutch is not even intelligible within itself, as the different Dutch lects often cannot understand each other well. It’s the same with Flemish. A number of the regional Flemish lects cannot understand each other well.