It isn't any mistake you're making with the commands. I'm not sure why he keeps saying that.
Reboots are almost definitely caused by the ric security service on your device which will force your device to reboot when /system get mounted as r/w. I don't know how to disable ric on Lollipop with a locked bootloader and can't try because my bootloader is unlocked, which does disable ric.
Try to root with KingRoot, then reboot your device before running the script.
Also, you can make sure you have the latest KingRoot 4.1 from its thread on XDA
here. It says the latest version will disable ric, but I haven't tried it.