The two groups had agreed not to bother each other and to keep their current distance while traveling, but they were still cautious of each other because while there didn't seem to be hostility, it didn't change the fact that they were strangers and it was unknown if what they had said was true.
A powerful expert has the ability to discern when someone is lying or hiding something, but with Oliver's presence in the group, it was difficult for Ecclesiastes to identify if Andrew's words were real or if he was hiding something from him.
For Oliver, it was the same situation. Although he is more powerful than Ecclesiastes, the difference is not abysmal enough to be able to read him fully. Ecclesiastes returned to his caravan before the half-hour he had asked for was up.
