Is what my 6yr old son is doing weird?

Lately my son has a fascination with sucking on my husbands navel like a pacifier. The first time he did it is when my husband was changing his clothes. All my son said was it tastes salty. We didn't think anything of it and just chuckled. However, lately I notice he tries to do it more often. I yelled at him to stop doing that and he started crying. I don't know where he got this from.