Squire Maxson was sent to the Citadel after Lyons went AWOL, since it's described as 'recently'. Maxson would have noticed something was amiss, I would imagine, and contacted the Elders, including the information about the Outcasts. For that matter, his MOM would want to know what was going on, hence a reason for communication, if only because he's a BLOODY MAXSON.
Actually:
Born -- 2267
Died --
Only son of Jonathan and Jessica (both deceased).
Last of the Maxson bloodline.
As an infant, sent to the Citadel to be fostered by Elder Owyn Lyons. The reason for this decision was two-fold:
1.) Recent internal conflict amongst the Western Brotherhood of Steel created an unsafe environment for the child. It was believed that the Citadel -- despite being located in hostile territory -- would increase his probability of survival.
2.) Elder Lyons, at that time, was in high favor with the Western Elders, and deemed a perfect candidate to provide care and training to the Squire.
Recent events have led to a lack of communication with the Western Elders. As a result, Squire Maxson will remain at the Citadel indefinitely.
Emphasis mine.