It's awfully hard to figure out how these could be handprints made in hot lava. If the rock is a basalt, as indicated, look to the Hawaiian eruption going on since 1983: The flows run around 2,000 degrees F at the flowing liquid surface. Once the surface of the flow cools just a bit, a rough, clinkery "rind" forms atop the still glowing lava beneath. Seeing a smooth "non-clinkered" surface seems pretty rare (but I'm not a volcanologist!). Looking at the other patterns in the picture, it looks like ripple marks are present on more or less the same plane as the prints. Not perfect ripple marks, but enough like them to make me wonder. Lavas often do end up intersecting water (again using the Hawaiian eruption still going on as an example), and seeing a rock record of interlayered lava flows and sediments, even fine-grained silts and clays, is entirely normal where basaltic lava flows often occur in underwater rift basins. So, perhaps the handprints are impressed upon a thin layer of ripple-marked silt itself resting upon the surface of a basalt flow. One thing it seems unlikely to be is human handprints impressed on still-molten lava.