Q: Can my assistant coach sign recruits for me?
A: Yes and no. If you have not made any recruiting efforts for the current recruiting period and have more than 3 scholarships open, the assistant coach will fill all but 2 of the open scholarships (maximum of 5 signings). This is by design to assist coaches who were out of town during recruiting and to address schools which have been abandoned.
That doesn't really answer the question why the assistant coach felt the need to go sign players for you. I imagine that was a bit of a glitch. The question that I have is whether you had contacted the players that were recruited to your team by the Assistant. Do you have any idea whether they have any talent? My guess is that you may regret having them after this season, but not be able to rescind their scholarship without a loyalty hit.