He didn't repeat it because he knew it was wrong.
He didn't repeat it, or indeed state it before the LBC interview because it was not his position. He wasn't making policy stance up on the hoof...
It is very clear that his response was
very carefully considered prior to any interview whatsoever for several reasons:
a) He is not Corbyn. He is a serious contender for next leader of a first world country, not a 1970s throwback in a Fidel Castro cap leading protests and Glastonbury appearances and enjoying getting his name chanted in return.
b) If he is to be PM in, possibly, six months, he has to think about his alignment with other world leaders, especially European and NATO. If you look carefully none of them are calling for ceasefire, but are calling for humanitarian pause, which is exactly what he is doing.
c) He has to think through the consequences of what he says, and in particular how it would shape the responses from others both nationally and internationally.