Redirect 404 pages to a other page

I have something really strange. When you go to this url:

https://www.offirent.be/faq/blablasqdurlnotexist

(of some other

I am directed to a article in easyblog

I have found out that it is this page:

https://www.offirent.be/diensten/vergaderruimte-te-huur

or this post in easyblog.

https://www.offirent.be/administrator/index.php?option=com_easyblog&view=composer&tmpl=component&uid=7.185&return=aHR0cHM6Ly93d3cub2ZmaXJlbnQuYmUvYWRtaW5pc3RyYXRvci9pbmRleC5waHA%2Fb3B0aW9uPWNvbV9lYXN5YmxvZyZ2aWV3PWJsb2dz

I was thinking it has something to do with my template, but even in the standard templates I have this strange behaviour.

Is this a setting in easyblog what I can not find?

Thank you,

Davy

Ps. When you go to this page https://www.offirent.be/diensten/blabla you get a other easyblog page.