The birds spit acid and explode into flames upon striking the ground (having become mutated and toxic due to, uh, global warming).
-- Wikipedia s.v. Birdemic: Shock and Terror, "uh" added
Q: Why use a codeword?
A: As a sort of perfunctory protection. Spreading "false" (i.e., true) information about the birdemic is already a crime in some countries, and we can expect more of that in the future. Dissent from the party line is definitely "denial," and probably "hate" to boot. While it would be a stretch to say that using the word birdemic provides plausible deniability, it does make what one writes less searchable. Even if someone thinks to search for "birdemic," which they won't, results relating to the 2010 James Nguyen film of that name will swamp out everything else.
Q: What have birds got to do with anything?
A: The corvids are a family of passerine birds comprising the crows, ravens, rooks, jackdaws, jays, magpies, etc. Their family name happens to sound a bit like the official name for the birdemic.
Q: Isn't this infringing on James Nguyen's intellectual property?
A: No. His film uses a capital "B."
Q: Does the actual movie Birdemic have any relevance to the current unpleasantness?
A: In a general sense, yes, in that the characters in the film seem inexplicably oblivious to the fact that the birds are obviously fake and that the story they are living in doesn't make any freaking sense.
A few scenes have more specific relevance. For example, the safety measures taken by the characters to protect themselves from the birds call to mind similarly effective measures recommended (or coerced) by governments today.
And of course, there's the famous "clap for carers" scene.