Here's something interesting to think about, Hiro probably knows more than we think.
1) Sulu is at a high level of whatever it is that's going on.
2) Sulu was trying to get Hiro involved in the company at a high level (obviously his future sucessor).
3) Remember how everyone else has discovered their powers? By accident. Remember how Hiro discovered his powers? He was already trying to stop time, it's a pretty big coincidence that he just thought he had the power to stop time and lo and behold, he's able to stop time. He clearly knew ahead of time what his power would be and was trying to use them, the logical conclusion is that Sulu knew what he would be able to do and told him.
1) Sulu is at a high level of whatever it is that's going on.
2) Sulu was trying to get Hiro involved in the company at a high level (obviously his future sucessor).
3) Remember how everyone else has discovered their powers? By accident. Remember how Hiro discovered his powers? He was already trying to stop time, it's a pretty big coincidence that he just thought he had the power to stop time and lo and behold, he's able to stop time. He clearly knew ahead of time what his power would be and was trying to use them, the logical conclusion is that Sulu knew what he would be able to do and told him.