Anything is possible David, but I have worked with wood for years and even when split in the manner you suggest there are still tells, usually shown in the end grain of the wood. Even though I can find absolutely no evidence of this method being used anywhere on this scabbard, if done with great care to detail what you suggest could still explain how this was accomplished.
Best,
Robert
P.S.
I have just taken a second look at the scabbard and because of the way the grain runs (it looks to be quarter sawn) splitting it in the manner you described before working the blade recess would be all but impossible to accomplish.
