That's a modification made by AKuHAK, since you're on deckard (from 7500X onward), so you're able to play Ps1 games (original and backups) from any region, but only if the ps2 is set to NTSC.
Previously (on MechaPWN force unlock mexico) if setting your Ps2 to DTL-H77004, you could only play PAL Ps1 games (or also NTSC games, but you'd need to patch the ISOs to europe region before, than burn a backup copy).
So he made the console to automatically switch to NTSC. It doesn't happen on 50004 (since on them you cannot play games from other regions).
Also on Ps2, Ps1 games video output is forced by the Ps2 bios setting. So in your case Ps1 PAL games will output in NTSC. You can solve this using Ps1VModeNegator or the modified Ps1 drivers.