I think Boris tried to explain that apparent contradiction, DM. In the first instance his only interest is himself, that's how he became aligned to the leave campaign in the first place. To that end he says a lot of things that a particular audience at a particular time want to hear e.g Ulster WILL remain British FOREVER under The Conservative and Unionist party and, of course, he'd prefer his corpse (presumably after being flattened by construction machinery preparing the new runway at Eefrow) to be found in a ditch (perhaps a ditch dug as part of the preparation of said runway) than to ask for an extension. Moreover, there is nothing to stop him asking for an extension in any tone of his choosing e.g. he could qualify such a request with a clear statement that his position (negotiating position, not his flattened corpse in a ditch) will not change in any circumstance. Hence Europe would have to refuse the request.