I'm not sure why this answer was voted down, since - I think - it answered the question. In a very simple way, I know. Anyway here goes my answer, which is basically an expanded version of the linked answer:
In order to share a wifi connection over bluetooth so that other devices can access the internet through this wifi connection, this worked for me:
Install blueman package.
$ sudo apt install blueman
From a terminal window, open Blueman Local Services:
Just fill the above window as specified and click "Apply" (if it is grayed, just change anything and revert).
Open Blueman Manager to make it easier to connect devices.
Then, to use this connection from my Android phone:
- Pair Android 6.0.1 phone and computer
1.1 Enable bluetooth
1.2 Enter bluetooth settings and make device discoverable
1.3 On PC, click "Search", find your phone and click the Keys button on the toolbar.
1.4 Confirm pairing both on your phone AND on PC.
1.5 Optionally you can mark this connection as "Trusted" by clicking the Star button on the Blueman Manager window.
- Enable network connection from Android phone
2.1 Enter bluetooth settings and click the area pointed by the following image.
2.2 From the screen that will open, turn on the "Internet access" option.
That's it. Within a few seconds, I had internet.
The procedure is very similar if you want to connect another device to the internet, such as a Windows PC. Just pair and enable internet through the connection.
$ cat /etc/issue
Ubuntu 17.10 \n \l
Bottom note: I know the OP asked for the procedure for a Raspberry Pi, but, as it is Debian-based, everything I wrote applies.