Yes, that is something that would be a realistic cause.
What you can do is practise good observation skills. Watch Bug and Nitwit closely, and if Nitwit starts 'posturing' like he is going to become aggressive (that includes staring, focused attention on Bug, the tip of the tail beginning to twitch, muscles tensing, stuff like that) or Bug starts showing 'defensive' behaviour before Nitwit starts being aggressive, at that time you need to interrupt the focus of their attentions. You can do this by throwing a toy their way, or breaking their eye contract or petting them, or picking up Nitwit - NOT Bug - and distracting him by cuddling or putting him in a different place, or putting yourself between the two of them, anything that will divert attention from each other, you will prevent another outbreak of aggression. You will need to be really vigilant because you don't want the aggressive moment to happen. The more it happens, the more difficult it will be to break it. You want to find ways to remind these two how good it feels being in each other's company. If you do pick up Nitwit, then after he is distracted, you can pick up and cuddle Bug, but if you pick up Bug first, Nitwit will view his being 'higher' as a threat and become more aggressive possibly.
Give them treats when they are beside each other behaving and try to reward them when they are good together. Be prepared to separate them and give them 'time outs' if they start getting 'posturey'. Pet them both together in each other's company and try to find ways to encourage positive interaction. Praise them when they play together, but don't yell or get angry if they do get huffy. Have a throw or a blanket handy that if you need to you can throw overtop of one of them or both as another way of interrupting aggression. It will then give you the means to effect separation without anyone getting hurt. Hopefully, after a few days of this positive reinforcement and distancing from the causative event, Bug and Nitwit will start to behave more like old buddies and less like competitive strangers.
I would still recommend getting either or both of those books. Good luck