Oh aye, this much was obvious at the time. Same applied with his non-specific rhetoric about cutting welfare. He didn't think he'd win an overall majority anyway (why should they have, they were bloody awful for five years) and so once he went into another coalition, they could get rid a load of the rabble rousing right wing crap that got the blue rinse brigade all excited. Just say the other lot won't let that fly, the bastards. Only then they erm, won.
Even if he decided he was bound to his stupid promise, there were so many better ways to do it. I think he actually went ahead with it a year ahead of schedule, the ham faced moron.
As for "not leading a Government that wouldn't hold a referendum"...riiiiight. How would he have possibly got one through a Cabinet where he'd have had to use Lib Dems (presumably) again? Which other coalition partners was he thinking that he'd have? Pretty sure only UKIP were expressly anti-EU at the time and they had zero chance of getting to that point.