I didn't read it that way at all. That last paragraph seemed very polite and respectful, and keeping up a polite relationship will almost always be mutually beneficial to both parties. I find it hard to see politeness to be petty even if it is done out of a certain self interest. It might be an apples-orange comparison, but I think seeing this kind of shmoozing as petty would be like seeing doing public service to bolster a resume or something as petty; yes, there's a motive other than some absolute purity of heart nonsense, but denying the ends and means as petty because the motive isn't sacrosanct seems like the actually petty line of thinking to me.

I also care about the "good of the world," but I think aligning self-good and global-good is a perfectly acceptable reason for doing things.

TL;DR: No, you shouldn't always act out of self interest, but you shouldn't have to deny self-interest in order for something to be considered "good."