As the Tor community knew of a possible compromise in advance, what what is the purpose of this? Sounds like fear mongering by the TLAs with the aim to discredit anonymity within the network rather than actual malice.
Also, warning people not to use those mirror sites is a responsible reaction to possible compromise.
Other than that, I agree, I don't see what the point of this would be. Especially when there was some early warning. It is possible that the warning from a few days ago is entirely unrelated to this incident, though.
Maybe this is related to the Sony hacks, the authorities could know about a forthcoming data leak or threat. Taking away a major source of anonymity could prevent the information getting out.
Also, IMO it's unlikely that these events are unrelated.
1. Tor says they might get compromised.
2. Guy's exit node gets compromised. an attempt to incapacitate our network in the next few days through the seizure of specialized servers in the network called directory authorities.