While the time bastard is a possibility, it is a theory not stated in the game. It is somewhat implied, but there could be other possibile explinations. Besides, I'm not suggesting that he couldn't, but that he would have no reason. Also, time bastard would further support my theory that Magus would have no reason to venture to the dbt, because
if he time travels and becomes that Magus, he would replace it's knowledge and remeber that no matter what he does, he will change nothing.