If those players do NOT show up in your recent friends list, then these are Blizzard bots. Those are legal, Blizzard created them to help players get into a game when waiting for a human opponent in the same mode and at the same skill level would take too long.
If these players DO show up in your recent friends list, AND you are sure they are bots, then those would be illegal bots. Please report them using the recommended method: