Thanks Clare Prop #118
It comes down to “in proximity” WRT the correct frequency.
The hypotheticals regarding reciprocal headings etc. are fair but could happen anywhere where there are airfields close together. Is YBEV having a CTAF shared with White Gum and Northam the answer a la YMUL and YSEN, not convinced due to over transmission and frequency congestion.
After your description about the tow plane incident, certainly rude, but not necessarily a function of it being a tow plane.
The YBUN CTAF call was from about 6 years ago, perhaps the transmitting pilot had finger trouble.
Going back to YCAB, is the assumption that both planes were on the CTAF. Others have reported frequency congestion from adjacent fields.