You known this, or you're just suspecting this?
I suspect.
I met Tim at PAX, he didn't want to share much, all he said was that "we have the original game assets, not all the artwork, we do our best to make it look good in HD".
My question was if they had the original drawings made for the game (that were more detailed, like monkey island 2).
But I'm a graphic artist.
This is not the result of art, but post process :
That greenish outline is the result of pre existing anti aliasing. It's very subtle and very high quality vector conversion.
And those gradients don't seem like they have been hand picked by an artist at all.
And on almost every animated objects in the game they did redraw it, tracing vector over the original and fixing some shapes.
Sadly, while it did make easily identified details better , it also left the new artist wondering what was going on, like here, what the hell is this :
Also, the black shadows are 99% identical to the existing ones, only a tad smoother.
Speaking of which, the characters cast no shadow.