Sorry, I misunderstood you. No, it's doing exactly what he's telling it to so - send his email to everyone in the To:, CC: and BCC: lists in the email he's responding to. I normally don't carry on email correspondence with more than one person per email (that's what chat and forums are for), but the few times I've done it, when I didn't want my replies in the inbox I've either just deleted the one sent to me, or I've deleted me from the list before responding. (It's easy to highlight your name and the comma with a mouse - on a phone I'd try to position the cursor at the end of his name, then backspace to get rid of himself in the list.)
But the program is doing exactly what the protocol calls for it to do. Even with Listserv and derivative email list servers you get a copy of your own emails. I don't think they're going to put a checkbox reading "Don't send an email to me even if I'm in one of the addressee lines" in any email program. Those of us who were sending emails since before the internet was called the internet are so used to that, that we'd probably start having fits..