This is a common statement during the first season of K-ON!, also used in the second (but not so many times).
K-ON! is not a show about music, but a show about the girls who play it, finding their place through it and cementing their friendship with their instruments, sometimes, as an activity to hang out, more than as the real purpose of those tools, play music.
Since this happens, and the main activity of the K-ON club is taken as secondary, as a means to an end without a real meaning other than an excuse, a lot of people may take as a fact that those songs aren’t relevant, but I would like to differ. The show doesn’t talk directly about music, okay, but that doesn’t mean that it doesn’t touch that topic in other ways.
And one of those ways, I would like to think at least, is a creative struggle.