Probably a little of both. Two dates warrants an email break up at the very least. Honestly, I’d rather someone just blow me off entirely than send a text message. I can’t imagine a more impersonal way to be dumped. Maybe carrier pigeon. (Though that does require the dump-er to actually catch a pigeon and attach a note to its leg, which I’d say ranks a bit higher on the effort scale than tapping out “Hey, we shud C othr peeps” on your phone.)
His lack of a follow-up call or text (he didn’t even take the time to ask why or even type out “ok”) says he’s also ready to move on. Why do you care if he’s upset? If you cared, you should have put more effort into the break-up. Sounds like you may still have feelings for him.
If you’re worried about whether a text message break-up will annoy a guy, don’t do it. Email, call, write him on Facebook, whatever. You’re not required to call things off face-to-face with someone after two dates. (Though after four or five dates, you’re kind of a jerk if you don’t do it in person or at least on the phone.) That said, if you’re worried about a guy’s feelings, keep in mind that a text message shows a serious lack of interest and respect on your part. It’s also very easy to misinterpret a text message. (For instance, you aren’t sure if he’s writing “K” with a shrug or a scowl.) A nicely worded email is always appreciated, and harder to take the wrong way.
Wait, I thought of a break-up method worse than a text: Twitter. Do not break-up with someone over Twitter. I can’t think of anything worse than all your followers retweeting your break-up message to some poor guy.