Assuming Leoben was not lying, at an occasion where he had plenty of reason to do so (he was a cylon agent after all, why not sow a bit of mistrust right where it hurts), seems very unwise, though. He did, in fact, lie in that very episode about the nuclear bomb he had supposedly hidden in the fleet.
Whether D'Anna and RDM had also good reasons to lie when they made their respective statements, is another matter. Circumstances are quite a bit different though. At least RDM can hardly lie IMO about this mystery they have been building up for a long time, and I wouldn't know why D'Anna would be lying at a time when she is quite in charge of the situation.