You’re half right. FM receivers DO lock on to the strongest signal on a given channel, but this is variously called FM signal capture, the FM capture effect and other similar terms. Selectivity is the ability of the receiver to discriminate between signals on adjacent channels. In other words, if you have a receiver with poor selectivity tuned to 98.5, you might also be able to receive a signal broadcasting on 98.7 or 98.3.