Explorers - VERY difficult to spot

On Page 29 of the rules it states ‘Outdoors, explorers are difficult to spot, having the ability to seemingly disappear into woods and underbrush with a proficiency throw of 3+ on 1d20.’
Is 3+ correct? or should that be 13+?

It’s 3+. Explorers are hard to spot outdoors.
Explorers were based on B/X’s Halflings, which had a similarly profound ability to hide outdoors.

So this is not the roll to spot them, but the roll for them to “disappear”? Does this mean that if an Explorer makes their roll successfully, then you don’t roll for others to spot them, they automatically fail?; they’ve succeeded in disappearing and so that’s that.

So this is not the roll to spot them, but the roll for them to “disappear”? Does this mean that if an Explorer makes their roll successfully, then you don’t roll for others to spot them, they automatically fail?; they’ve succeeded in disappearing and so that’s that.<<
My interpretation: Yes. Its comparable to a thief’s hide in shadows ability. There is one exception: the explorer needs cover to disappear, but a thief can also hide without cover as long as there are shadowy areas.

Beastman’s interpretation is exactly correct.