It matches the VOL- button in that LIRC file.

If you have trouble with the RC5 dialog, it is also possible to directly paste in the RC5 Pronto hex (in place of the hex you showed above).

5000 0000 0000 0001 0000 0011

You can edit that string replacing just the last two digits of that with the last two digits from the LIRC data.

You can also get the IrTools program and DecodeIR dll from the JP1 group, and use those to decode learned signals from the longer Pronto Hex form you posted, to get the device and command numbers.