From the 1.6.0 Patch Notes:
“A fearsome and vengeful warrior most well-known for joining Liu Bu from Liu Zhang in 214 CE and his participation in the Southern Campaigns.”
Wei Yan never served Liu Zhang. Wei Yan was from Jingzhou and only ever served Liu Bei, joining the latter prior to the invasion of Liu Zhang’s land of Shu. In the novel he served Han Xuan, who again is not Liu Zhang, prior to killing Han Xuan and defecting to Liu Bei. He also did not join Liu Bei in 214; he joined closer to 209 and became a ranking general of Liu Bei in 214. Plus they put “Liu Bu” instead of Liu Bei.
So, no, he is not “most well-known” for any of that stuff as none of it, from either the novel or history, happened to him.