I think I know how he did this. Nothing special really. I have a lot of experience with PSP ISOs so here's my thoughts. I've seen the PS3 disc structure & it's exactly the same as PSP. PSP_GAME & PS3_GAME, USRDIR & SYSDIR. I think he just changed PSP_GAME to PS3_GAME, modified the PARAM.SFO a bit & launched EBOOT.BIN (or BOOT.BIN), thus starting the game (all PSP games boot from EBOOT.BIN or BOOT.BIN & we can boot such files with PSGroove). I know PSP & PS3 are 2 different systems but think about Mini's.
Just my thoughts. Can't test it myself because I don't have anything to hack my PS3 with
If anybody would care to try, that'd be great.