It has little to do with whether he believed her or not and all to do with the lack of clarity. Javert understood nothing of what has happened to him and where he ended up. He wanted someone to be straight and transparent about everything he needed to know in a way that made some damn sense, and he would prefer that information to come from another recognizable human being.

"No matter," he muttered. "You have given me something to go on, more helpful than the bag of bones with the rifle who greeted me first, or the hags who thrust these things upon me." He refers to the pamphlets in his hand. "Show me to Tsukikage, and I will speak to him."