These lines of code have nothing to do with the bootloader.
These lines tell the compiler to only compile code for your selected board in the boards manager.
Did you compile for an explorer and have the sodaq one attached to your pc? It will upload since it has the same microcontroller (different package) and ofcource it will not work, the pins are routed differently.
A failing RN2xx3updater sketch usually is the issue from having not the latest Arduino IDE + not the latest board files.
Use the SAMD boards url to optain the latest board files.
Install the Arduino m0 board files, then the arduino ide thinks it's an Arduino Zero. All Sodaq's SAMD boards have a bootloader based on the Arduino Zero. You can load Arduino Zero bootloader into any Sodaq SAMD board without issues. The extra features like fading led when it's in bootloader mode will not be there.