Hosoi claimed that he was facing down (see image) while pushing the the gate closed, but also that the wall that the gate would slide behind made it impossible to see anything until the last moment. One of the news clips shows that after a few moments, the area past the gate does come into view.
Hosoi wrote in his book that he sincerely believed he was just in his "police-like" enforcement of the lateness policy at the time. And while he claims to regret the loss of the life of a "precious student", his book, "Only the Clock Knows: My School Gate Incident" (referring to the clock above the gate, which would have a view to both Hosoi and Ryoko), it seems to me like he is still believes he wasn't to blame.
I admit that I haven't actually read the entire thing, though I was able to find some snippets and reviews about it. Though I would be interested to give it a read.
My guess is that he saw the first group of students pull up seconds after he started closing it, before the bell had stopped chiming and he slammed it. Students said that 5 seconds before 8:30, he shouted out "that's it, I'm closing it!"
I have a hunch that the gate had moved beyond Toshihiko's grasp by the time that it hit poor Ryoko. The investigation found that the speed of the gate was a major contributor to the severeness of Ryoko's injuries.
