As the comic story goes, Siddiq came from Miami, where he was living when the walker outbreak first happened, and he traveled up the coast until he reached the Oceanside fishing community, where he stayed for a while before later making his way to Alexandria.
And he plays an interesting role involving two other characters’ romance, but that’s not worth getting into right now.
A solid dude on most fronts, Siddiq was first introduced to Walking Dead readers at a point in the story that’s a bit later than where the show is now, comparatively, as it happens after the post-All Out War time jump.
But even though the details behind the situations would be completely different, there isn’t anything too important tied to the timing of his arrival, so it could easily happen a little earlier for TV without any big narrative problems arising.