I think you've hit the nail on the head - its because he can't control it. I think he may be afraid that you're getting advice, help and a friendly ear here, and maybe its stuff that he might not want you to hear...

And of course you're not wrong to use the computer. Just because he doesn't use it, doesn't mean you shouldn't. His choice not to, just as it is your choice to. He should leave you alone, esp as you've been 100% honest.