I recently flew with my dad to Narromine Ausfly, I flew a brumby low wing (very nice plane to fly btw) on arrival I contacted ground and stated where I would like to park and they directed to me to the appropriate area. Once I shut down I opened the canopy and had noticed a guy walking over to the plane in a yellow vest, I initially thought it was going to be a ramp check, turns out he wanted to do a breath test. But he walked over to the right side of the plane where my dad was sitting and wanted to breath test him, I found this quite surprising that someone from casa did not know which side the pilot sat, dad told him he wasn't the pilot and he was quite surprised and came over to breath test me, he also didn't realise that I was a minor and he then had ask my dad for permission for me to provide a breath sample. So I was really surprised on the lack of knowledge from this casa officer