In March last year, Sekoia modified the Mission Briefing template to only link to another page if the page already existed.
So, for example, since Positron has his own page, his name is linked under his picture in James Harvan's mission.
On the other hand, if you were to place a Mission Briefing on a page where Becky, the Tarantula Mistress is the NPC you're speaking to, her name would not be linked because she doesn't have a page of her own.
That being said... it looks like even though the link isn't being created in the name under the image in a Mission Briefing, there's something in there that's still making the wiki think there should be a link in there to that missing page. I tried changing one of the Taskmaster Carlyle breifings to Taskmaster Carlyle II and Taskmaster Carlyle II immediately indicated the mission was linking to it.
But it's not the image itself that's creating the link.