[greenbit]

Maybe it's the very molecules that the live cells were using, just doing their thing without the cells. Cells concentrate things by confining them in a small volume, but otoh, if you have damp particles, the thin water layer on the particles would be a kind of confining space, with the added advantage of surface area to exchange gases with.

[andrewflnr]

This is addressed later in the article. They think there's probably some of that activity but don't think those molecules could last long enough to produce the observed effect.