His attempt to find an explanation (as unlikely as it is) may come from the fact that his prestation on Hannity was a bust. Who goes on Hannity to complain about partisanship? So, he may be looking for another career.
Anyway, BMG has a good take about this excuse:
http://bluemassgroup.com/2013/02/scott-browns-hilariously-non-credible-explanation-for-bqhatevwr/
Now, with all due respect to ex-Senator Brown, that is a ridiculous explanation. You can conceivably put your phone in your pocket and then accidentally dial someones number (the pocket dial) or accidentally post a tweet; such a tweet would probably consist of a couple of nonsense characters like asdf that accidentally got pressed. But sticking your phone in your pocket whereupon it accidentally types bqhatevwr and then posts to your Twitter account no, that is not possible (or, more precisely, the probability of such a thing happening is vanishingly small). And the fact that bqhatevwr was immediately followed up by the correctly-spelled whatever shows that, in fact, a pocket tweet is not what happened. So, ex-Senator Brown is
embellishing, shall we say. Gizmodo goes into more detail about how bqhatevwr could not possibly have been a pocket tweet (key condition that would have had to be met: Scott Brown has a very bony butt).
What really happened is almost certainly this: Brown, irked by whatever it was that Michael, Bud Parsons, and Matt had to say to him, decided to respond by saying whatever to each of them. He hilariously mistyped that response to one of them, resulting in the now-famous bqhatevwr tweet (its unclear who he was talking to, since not only did he misspell whatever, he also did not include an @ to make the tweet part of a conversation with another user), and then continued with his weird series of tweets, culminating in the grammatically-incorrect Your brilliant Matt. Whether or not he was drunk, I have no idea he says he wasnt. But he surely was not pocket-tweeting.
I have no idea why Brown went to so much trouble to concoct a story that obviously makes no sense.