Why the same MacMini provides different MAC addresses for different OS? I run MacOS and CoreOS Linux on the same MacMini. The same network interface has MAC f0:18:98:ea:7f:9f under MacOS and has MAC 38:f9:d3:16:96:ce under CoreOS. First one is printed on a box of this MacMini, second one isn't. 

Why does it have two different MAC? 

MacMini 2018 gen, with T2 chip.
MAC addresses are assigned to network interfaces, not to computers. The F0:98:18 address is for the wireless card, and the 38:F9:D3 address is for the wired Ethernet interface.