Going on my page by phone was generating retina images no matter if the optioon was on or not.
I did some investigating and i think I found out that the check for the retina option in the imageReplacer() function in mavikthumbnails.php in the plugin is not there at Line 186.
(at least I fixed it for me there)
Maybe I have some misconfiguration somewhere else.
Anyways, if anyone has the same problem, maybe this helps.