He probably gave it to you in case you have to enter factory service mode. But since you're on 3.55, there's a software/app route to getting there now. Still, having a dongle for that is a great fail-safe.
CECHL04 has no PS2 capability at all.
See here according to your model #:
There are methods of playing PS2 games but, it's rather glitchy for PS3's without the Emo Chip. See here: