He maybe just stressed and feeling a lack of control. He may not be aware of the fact that he has made you a target of his frustration. Or, he may be aware that he is aggitated with you possibly because you have more freedom to come and go and don't have to work so many hours but not have the self-awareness to pinpoint the reasons for his feelings.
If you can take the high road and just tell him that you are aware that he is under a lot of stress and if there is anything that he would like to talk about with you, you can be a sympathetic ear, then that might be the route to go. But, if this guy just happens to be a real jerk, then I really wouldn't bother. Why set yourself up for his nastiness.
Wish I could be of more help.