Hi,

AutoCAD 2018 uses new (2018) drawing file format which also applies to template files.
But AutoCAD for Mac (most recent 2017 and earlier releases) cannot read files in new format, so actually AutoCAD opens new empty drawing instead of creating drawing from your template.
You need to save drawing template in AutoCAD 2018 on PC side in 2013 DWG format, than you will be able to use this template on Mac.

Maxim