I initially figured it was condensation from the agar. But it is not on your lid and you said you suspected humidity was low.
I found this here http://www.gettyimages.ca/detail/photo/mold-penicillium-vermiculatum-growing-on-high-res-stock-photography/128606087.
with this caption
Mold, Penicillium vermiculatum, growing on agar. The water droplets on
the mold are part of the respiration process of the mold.
Those droplets do look like pure water. And oxidative metabolism does produce water:
CHOH+O2 -> CO2 + H2O. It is interesting that the top of the mold is so hydrophobic that the water forms little balls. Why might that be? If you know, comment please.
Other fungi might put stuff in the exudates that collect atop them. I read that some aspergillum species collect droplets of purple exudate on old colonies but I could not find good images. Here is another penicillium with amber looking exudate. These exudates can contain metabolic products.
Exudates (or Extrolites): Some fungi can produce exudates as a
by-product of their growth, many of which can be collected for
commercial use. Mycotoxins are by-products (secondary metabolites)
which are potent poisons. Penicillium citrinum produces Citrinin, a
nephrotoxic mycotoxin which derives its name from the fungus. It may
also produce other extrolites such as tanzowaic acid A,
quinolactacins, quinocitrinines, asteric acid and compactin.
If these fungi were spreading out in their natural habitat of rotten stuff, the secreted mycotoxins would be clearing a path for them, wiping out those organisms that dare compete for that rotten stuff.