Radio Calls
The other possibility is that the C172 gave a "turning final" call just as the -8 gave an "entering runway" call cancelling each other out. We have had it here a couple of times, fortunately all without major incident. If you stick to the required calls (CAR166C & CAR243 + CAAP166-1(1) sec.6), i.e. C172 only gave a joining circuit call then maintained a listening watch, the -8 gave the entering call then the C172, upon hearing the -8 could give a warning "on short final" call. Too many radio calls is dangerous, make the required calls and listen, then respond where appropriate.