Um, does it say that they should be discouraged from following up on these rumors until they reach 4th level? I mean, maybe I have weird players, but they tend to follow up pretty quickly on rumors that interest them, which, given this reading, would put me in a situation to decide to alter the encounters to be appropriate, fast track the milestone leveling, or invent stalls to prevent pursuing the rumors, all of which distort play. I suppose it's possible that the normal group of players do not attempt to follow up on rumors for a bit, but I find that unlikely. Which then means that the reading you're both advocating can often lead to distorting play experiences. I'd rather assume it was an unintended type than intentional design.