I have run a Network Scanner app from my android tablet to see the devices in my network and for my tablet it is written (in results) besides the IP address of the tablet and MAC address for the tablet also:
"only goes through [some other Mac Address]?"
question mark at the end of the sentence.
This other MAC address is not MAC address from the router, so I am wondering, what is it.
If anybody knows, please answer.
Every device that connects to your network has to have a MAC address. In order for anyone to tell you what that device is, they would have to have some kind of access to your network. Anything else would be guessing.
Because everything has to have a MAC address, you will need to be a detective to figure it out. What else is in your home that uses the Internet or the Network. A SmartPhone? A Network Printer, either wired or wireless? A Desktop Computer? A Bluray Player? A Smart TV? and the list goes on and on.
Without knowing anything about the app you used to do the scanning, I can't say what the developer meant by "only goes through [some other Mac Address]?" But the first three octets of a media access control (MAC) address identify the manufacturer of the network interface controller (NIC) with which the MAC address is associated and there are a number of sites that will allow you to provide a MAC address or partial MAC address, i.e., the first three octets, which are the groups of two hexadecimal digits usually separated by a colon or a dash, to identify the manufacturer.
E.g., you could look up that address at Vendor/Ethernet MAC Address Lookup and Search, which may help you identify what type of device has that MAC address. For instance, if I look up 00:09:6b:19:38:a5, I see the vendor listed as "IBM Corporation". When I look up 00:17:a4:26:88:d5, I see "Hewlett Packard aka HP (was: Global Data Services)" listed (the address was associated with an HP K5400 printer). But you only need to put in the first three octets, e.g., I could just search on 00:09:6b for the first example.
Keep in mind that the manufacturer of the NIC isn't necessarily the manufacturer of the device in which it is contained. E.g., if I lookup up d4:9a:20, the first 3 octets of a MAC address for a MacBook Pro laptop, the manufacturer is listed as "Apple, Inc", but if I looked up 4C-72-B9, the first three octets for a Qualcomm Atheros AR8152 PCI-E Fast Ethernet Controller in an HP desktop system, I see "Pegatron Corporation" returned. But you may be able to identify the device associated with the mystery MAC address by that method.
Also, in case you aren't aware, MAC addresses are not transmitted across the Internet, so no one can reach any of your systems based on a MAC address. They are only visible within your Local Area Network (LAN).