Questions about Thud:

I've had some trouble trying to figure out the context and meaning of these lines, so I'll like to ask for help here:

On page .245 it's stated that the dwarf who just spoke to Vimes sounded like "the one that had, he'd admit, been of diplomatic help downstairs". I've read the scene where Vimes is in the club under Pointer and Pickles with mr Shine, and there is no mention of any voice that has been of help to him.

On page 270, Vimes says that someone could have a motive to steal the painting if they found out the secret of Koom Valley and didn't want anyone else to find out. The curator replies that it would be a "coincidence", "It's not as if anything has changed just recently. Mr Rascal didnt turn up and paint another mountain!" What does he mean by that? Why would Rascal have painted another mountain if someone had just found the secret of Koom Valley?