Not unheard of, if it's a 'soft' blockage, i.e. a plug of tissue and waste, then sometimes the head of water behind it can slowly move it to a point where it will start to disperse and wash away. I'd keep an eye on matters though, any sign of WC's not flushing, or traps gurgling, investigate sooner rather than later. May still be an underlying cause if it recurs.
If soil pipe can be extended through the roof, then great, AAV's have their uses, but drains need to breathe.
