You have no proof. The game's engine was written by the same people, so it's likely to share the same problems.
You honestly think that Skyrim's engine is all new? I'm pretty sure that Todd Howard himself stated that it's an updated Gamebryo engine in an interview. Anyone with a grain of sense can tell you it's still the Gamebryo engine. Once the CK is released, we will know for sure, but I can say with certainty that the engine is not all new.
Considering that many of Skyrim's bugs and glitches are the same glitches we saw in Oblivion and Fallout 3, do you really think Bethesda would write a new engine with the same exact problems? Mind you, the save file issue isn't new, it was also experienced in the PS3 version of Fallout 3.
Edit: Also, even if the engine was all new, it wouldn't be "written by the same people", considering Bethesda didn't write the Gamebryo engine, they licensed it for their games.