Meta-fiction is a type of fiction that addresses the fact that it is fiction. Usually, fiction pretends that it is real. See Spot Run doesn't ask you to think about Spot's status as a fictional character or the story of his morning jog as a made-up narrative. On the other hand, meta-fiction addresses the fact that it is fiction. When Buddy refers to the plot, or to his "characters," or to the fact that he is sitting at his typewriter typing this out, he's being meta-fictional. Now onto the bigger stuff.
Though the style of both "Room Beam" and "Seymour" are markedly Salinger, there is also a clear distinction between the two – two distinct flavors of Salinger. The most obvious difference is the sophistication of the prose in "Seymour." We're talking sentence length (way longer), word choice (way more "Dictionary Required"), syntax (more complicated), and number of just-can't-help-himself parenthetical remarks (off the charts). If you want an example, read the first two paragraphs of "Seymour: an Introduction." That'll get you about ten pages in and you'll see what we mean. Or, start with the first sentence:
At times, frankly, I find it pretty slim pickings, but at the age of forty I look on my old fair-weather friend the general reader as my last deeply contemporary confidant, and I was rather strenuously requested, long before I was out of my teens, by at once the most exciting and the least fundamentally bumptious public craftsman I've ever personally known, to try to keep a steady and sober regard for the amenities of such a relationship, be it ever so peculiar or terrible; in my case, he saw it coming on from the first. ("Seymour" 1.1)
Many critics (John Updike among them) have criticized "Seymour" for what they consider to be showy, pretentious, self-indulgent writing. (Think about the sheer number of intellectual parenthetical asides. Not to mention the footnotes.) Some think Salinger took his particular writing style Salinger. Consider the following passages. Are they playful, or secretly self-congratulatory? Take a look, and let us know what you think.
I privately say to you, old friend (unto you, really, I'm afraid), please accept from me this unpretentious bouquet of very early-blooming parentheses: ( ( ( ( ) ) ) ). ("Seymour" 1.1)
There are, however, readers who seriously require only the most restrained, most classical, and possibly deftest method of having their attention drawn, and I suggest - as honestly as a writer can suggest this sort of thing - that they leave now, while, I can imagine, the leaving's good and easy. I'll probably continue to point out available exits as we move along, but I'm not sure I'll pretend to put my heart into it again. ("Seymour" 1.1)
I gave what I think are the two main reasons I've elected to get up, rise, from them. And I'd prefer to pack both reasons into the same paragraph, duffel bag-style, partly because I'd like them to stick close to each other, partly because I have a perhaps impetuous notion that I won't be needing them again on the voyage. ("Seymour" 1.9)