No, just the theory that some "bug in software generating private keys" made those funds unavailable. It's possible he transferred the funds to wallets he doesn't control, but then you can't call those keys "lost". If he did transfer funds (and I don't believe it), there have to be be some other reason why would he do such a thing. There are much more logical explanations what happened, like (in other from the least probable to most probable):
- hackers have been using transaction malleability to steel 1000 bTC a day through 2.5 years, and went unnoticed;
- Mark Karpeles transferred the funds to some other entity for any possible reason;
- hackers or the corrupted employe broke into their "cold" wallet and grabbed the coins;
- the alleged leaked document which states 750.000 BTC are missing is wrong, and those coins are still in control by Mark Karpeles & his associates.

Pick an explanation you believe most, but don't believe they had trivial error in code which genereted invalid keys. However incompetent they are, that task is too easy and that scenario is unbelievable.