No, because they existed in Warcraft2 but you ignored that (not to mention they had already established lore before Warcraft3)
It seems you forgot that Warcraft3 was released in 2001, TFT 2002 (the expansion), stating they will be added in 2003 as fifth race is evident to my point of view (after war3 release) not yours...
Because Chris Metzen is one of 3 co-leaders of Blizzard back then, he is literally 1/3 of the company POV back then, so yes it is not a small thing he post in forums