It would be a pretty far fetched illusion. But the point is that Estinien did confirm what the WoL said and the WoL already had pretty solid trust with both Aymeric and House Fortemps. More to the point, wether they believed or not, rumors were almost certainly going to start spreading among the lower classes and now Nidhogg was dead, the Dragonsong war seemed likely to start to reach an end. That common enemy had kept most of the tensions between the classes supressed due to the necessity of survival. With that necessity gone there now held great potential for major civil unrest. Aymeric saw this and knew that any action would have to be taken sooner rather than later to avoid bloodshed in the streets.

Its worth also noting that Estinien's true hate was for Nidhogg and for very specific reasons. He wasn't a fan of dragons but he didn't outright hate them, particularly after he learned and saw what he did in the Churning Mists.