Classic LucasArts artwork turned into movie posters

The latter, I assume.

By the looks of things, they're resized, cleaned up and remastered versions of the original box and poster artwork.

You read the article. That picture is a day of the tentacle poster using the Star Wars motif. They are posters, "most based on original artwork lifted from an era...". If you visit the link, look at the pictures, and know at least a few of the games, you'll see that what he has done is some fantastic touch up work on original artwork from boxes and that sort of thing, enlarging the art and removing logos, trimmings and small print where necessary to produce a high dpi, super large poster sized image. I grabbed the Sam and Max one for myself, and the detail is so perfectly matching of the original art I find it hard to believe he repainted it, but seeing I own the box still I can definitely say it's not original art by him. It must have taken a lot of work, and was a true labour of love, but original creations they are not.