what the forget happened in 20 pages
what is an ARG
what's with the pyro blog
what happened in the update
why are some people saying theres a show and some aren't
ARG stands for Alternate Reality Game. It's the same thing Valve did before for Portal 2, where the community participates in some sort of scavenger hunt featuring complex tasks that reveal clues about upcoming events.
The Pyro's blog post was a series of "mmphs" that came in two forms -- long words and short words. When these are translated into morse code the blog post reads "Monday" (or, including the title of the post, "a Monday"). The post was made on 6-22 at 15:00 PDT, which corresponds to the numbers written on the Damaged Capacitor (6.22V1500), one of the many mysterious "junk" items that have been dropping in TF2.
There have been no updates since the banana fiasco in which crafting two banana peels (another "junk" item) gave special error codes that constructed a set of QR codes leading to pieces of a document where Saxton Hale is being tried for the disappearance of monkeynaut "Poopy Joe" and America's entire supply of Australium.
There's a promo page on Adult Swim's website claiming that they and Valve are teaming up for something, and since Adult Swim does television, people are automatically believing it to mean that a TF2 TV show is in the works. Adult Swim has claimed otherwise, but some are still wary to believe it.