My knowledge extents are that cast pistons and semi-forged have the same initial manufacturing process, but then a semi forged is dipped in something providing a super strong surface on the top and sides of a piston, giving a forged like surface where wear and tear is prone. Forged is of course one big solid dense mass on top, sides, underneath, everywhere. A semi-forged provides faster expansion in bore than forged, lighter and quieter than fully forged, and yet they provide a stronger and more resilient piston than a traditional cast item. A very good middle ground and perfect for mass produced high performance road vehicles. Strength, lightweight, resilience, quietness, cheap...
As for hatching, yeah, who knows. Yours didn't have them, mine don't, yet some people are adamant that they do. Bit of an anomaly really. Maybe some factories buffed them out afterwards, who knows...