I don't know how these things work, but I think he means that what they built with Gamebryo tech (their inhouse version, not the same version that Divinity 2 uses for example) is theirs, but the Gamebryo licence is still Emergent Technologies' (or who ever owns it) - and that they've continued to build upon it, obviously, to the point that they call it "brand new".
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If Bethesda's community manager didn't say that its brand new (several times I might add... see the links in my other post) I'd humor such speculation since his semi-cryptic statement is in fact hard to interpret. However we know for a fact, a 100% fact, that the engine is brand new so hes clearly not talking about GameBryo. Besides, when someone says something like "The technology is ours and it is inspired by the technology we have"... hes talking about two different things right there. The technology that is theirs.... and the technology that they already had.
Of course the new engine is almost certainly based heavily on GameBryo because they don't want TESV to feel toooo different. However its abundantly clear its a new engine built from the ground up... so clear in fact its been confirmed, more then once.