The FreePBX Distro is maintained and put out by the FreePBX.org project. Lots of other companies will bundle FreePBX GUI on their own LAMP (Linux, Asterisk, MySQL, PHP and Asterisk) stack but that does not mean those systems are the Official FreePBX Distro.
Below are steps to determine if you are using the Official FreePBX Distro.
Optionally you can open the System Admin Module in the GUI and view the version number there:
What do the Version Numbers mean?
The FreePBX Distro Version Numbering System tells you at a glance what the core pieces of each track are.
In the example below, FreePBX Distro 10.13.66-2, let us recognize:
10.13.66-2 - The first number 10 represents the Major Track Number
10.13.66-2 - The second number 13 refers to FreePBX 13 GUI
10.13.66-2 - The third number 66 refers to Linux OS 6.6 operating system
10.13.66-2 - The final number 2 is used as the Minor Release Revision of this Major Track Number