You seem to be misunderstanding the reason I mentioned a microUSB to ethernet adapter, with one of those and a standard cat5 cable you would simply plug into the same ethernet device the RPi is connected to and access it directly using that network, no wifi hotspot is needed. Plus the tablet would have proper internet access to the outside world the same as the RPi. That would be your best "single" wire solution.
You just can't do what you are wanting to do without disabling hostapd and adding more software, like a DHCP server daemon (which is going to conflict with the DHCP server you already have on your network). Right now when you plug in a USB cable to the RPi, hostapd (the software that sets up the wireless access point) is assigning you the same address (192.168.50.x) as if you are a wireless device on your RPi.
It needs to be an IP address on the same network as the RPi (probably 192.168.1.x), not 192.168.50.x and even if you went into the hostapd configs and modified it to be on the same subnet it still wouldn't forward traffic properly. It just isn't meant to be used like that.
You'd be better off plugging in the USB to a router, if the router supports such a connection, it would at least have the correct DHCP configuration and assign you the correct address.
Most likely you are not running a rooted Android so trying to analyze what is going on inside the OS on the tablet is near impossible.
It just isn't worth bothering with when you can just get an adapter and plug in a cat 5 cable and it would work exactly like any networking device in the entire world.