Yes, Vahl was kinda 'mean' for an Acolyte.

But yes, he did not care for thieves at all. There is alot of history behind this, one of which was him warning the then Captain to not befriend Gacsoele(thief that led party into hell if you recall), and it turned out that Vahl's warnings were not heeded and Gacsoele got the taint afterall and everything was a mess. Aside from this, he believed that only one form of thievery was permissible, and that was thievery done by one who carried the light in their heart, which you did not.

On a side note, he never accepted any loot from you, or any other thieves who were not good. (that I can recall knowingly)

There was a bit of peace at the end, at least a lack of utter conflict. The guild burning thing was part of Vahl's role regarding going off the deep end of the rage pool as he got older and older.