After being denied full assistance by both Gregory and Ezekiel, Rick has a need to find strength in numbers, and the constant in-pouring of greyscale survivors in the final minutes could absolutely create a formidable army, if everyone’s interests align.
And though we know that The Kingdom and Hilltop Colony will eventually become one with Alexandria’s plight to destroy Negan’s rule, all of these newbies create quite the interesting wrinkle in how it could all pan out.
On the one hand, Rick might be smiling because he foresees a future where he convinces this locked-and-loaded community to join his mission to take down Negan and the Saviors for good, even though he has no clue of their own potential relationship with the tyrant.