Because since the weekend, we've been running under the assumption that the second special was titled "Wild Blue Yonder" because… well… that's what the BBC told us it was called in all of their press stuff and social media posts.

Source: https://bleedingcool.com/tv/doctor-who-rtds-wild-mild-typo-now-we-dont-know-what-to-believe/

David Tennant's Doctor will take centre stage in three specials we previously learned will be titled "The Star Beast," "Wild Blue Yonder," and "The Giggle."

Source: https://comicbookmovie.com/tv/bbc-america/doctor-who/doctor-who-trailer-for-60th-anniversary-specials-reveals-donna-nobles-fate-and-the-celestial-toymaker-a205823

The upcoming episode, "Wild Blue Yonder," will escalate the tension and include external dangers, promising a adventure with severe and emotional consequences.

Source: https://screenrant.com/doctor-who-tardis-donna-14th-doctor-location-clip/