The FreeBSD license has a copyright notice, one line with two conditions, and a warranty disclaimer. After having to read some other contracts and license agreements, this one is quite easy to get through. This is known as the 2-clause BSD license which is a derivative of the 3-clause BSD license.
IANAL, but the BSD family of licenses are known for being ...
The Github file you linked to clearly shows the license was modified, and that pretty recently:
@levitte Change license to the Apache License v2.0 1513331 on
Dec 6, 2018
The license before that seems to be some custom stuff, known as the "OpenSSL license", which may not have been compatible with GPL (2 or 3).
And the docs you link to has the footnote: