Some people loosen their rocker arms in the off season so as to relieve spring pressure on the valves that are held open.  But you normally see this on bigger roller cams with big spring pressures.  Your stamped steel rocker arms and the valve springs don't look all that agressive...but the seller may have loosened them since the motor was to be sitting idle for some time, perhaps.

The rocker nuts are "polylocks" for adjustable valve train but by themselves do not determine if you have hydraulic lifters or solid lifters.  Expalining that one via the internet to somebody that has no idea on how to tell the difference might be a bit tricky...

LO