The Sins were in the boar hat when they noticed an aura near by, it wasn't too intense but if wasn't weak, maybe mid-high level holy knight

Diane: Why are we going to the aura?

Meliodas: Bored, plus we didn't recognize it He shrugs

Merlin, Escanor & Gowther: They stay quiet

Ban: Sounds fun~

King: Of course you find it fun.

Elizabeth: What of they're a bad guy..?

The then see the source of the aura, it's a person obviously, the person seems to instantly notice them