AFAIK the standard TM mats use a flat Velcro disc that is screwed into the carpet floor. The underside of the mats have a matching circular Velcro patch. No grommets, hooks, drilled holes or the like. You were probably seeing the plastic disc with the small screw anchor.
FWIW, for some odd reason the circular Velcro area on the underside of my drivers side mat closest to the seat peeled away from the mat and appears to only be held by adhesive with a circular perforated cut out. Thus the mat was only being held by the Velcro at the top under the pedals. So the mat was sliding up. Dangerous a la Toyota/Lexus issue. I stopped by the Dublin SC and walked in with the mat. They took 1 look and brought the car around and replaced both front mats. No car manufacturer takes the front mat issue lightly...a major safety/liability issue.