I don't know what the student thinks but "[list of many problems]" are in some ways less "grand" as they are less about fundamentals of nature compared to the problems in quantum theory. But then Feynman puts "grander" in quotes to reduce its power and imply that "grandness" isn't all that - well - grand. He does this as his advice is that all problems for which you can find solutions are indeed grand problems. That's how I read it.