You can't install/use the themes from this PPA because they are TOO OLD. (Just look at the upload dates!) They support only the older GTK+ versions of older elementary OS versions. elementary OS Loki runs with GTK+ 3.18, so you can only use themes supporting THIS EXACT GTK Version. Not GTK+ 3.14 (Freya) or earlier, not 3.20 or later (actual Ubuntu/Gnome versions).
It is NOT recommended installing a newer GTK version on elementary OS as it WILL break some looks and functionality on your system.
There are OSX-Arc themes on gnome-look.org that DO support GTK+ 3.18 but they break correct Wingpanel behaviour and will introduce a bug into Pantheon Photos (non refreshing background).
AFAIK OSeArcLight is the only 3rd party theme at the moment that properly supports elementary OS Wingpanel, panel GTK widgets and Photos. Please note that it is still a bit buggy with GTK dialog windows and Granite apps. Otherwise usable. ... I know because I made it. =)
Also better not use a PPA just to install a theme. You can simply unpack themes into a hidden ~/.themes folder (or create it in your Home folder first).