Zero Snippets for printer.cfg leads to an klipper error

[Oellness]

Hi

I have a problem with this zero toolhead snippet for the printer.cfg:

[probe_eddy_current btt_eddy]
sensor_type: ldc1612
#z_offset: 3.5
i2c_mcu: extruder_mcu
i2c_software_scl_pin: PB10 <-- klipper error
i2c_software_sda_pin: PB11 <-- klipper error
x_offset: -19.8
y_offset: -0.75

If i use it klipper tells me that the i2c pins must be on the same mcu.

So after some research if found two solutions for these pins:

1. use "i2c_bus: i2c2" instead of the pin definitions
2. use
   i2c_software_scl_pin: extruder_mcu:PB10
   i2c_software_sda_pin: extruder_mcu:PB11

Both solutions work for me but i would like to know why?
It seems that for all other users the original snippets are working, but why not for me?