4. Who the cable is to: Secretary of State in Washington.
5. General subject heading.
4 is right(ish) - well, not even a marxist media studies graduate could be expected to get "to" too wrong. Info, on the other hand, means, well, what? It clearly isn't what the BBC claim - a subject heading (that comes further down under, surprisingly, the 'SUBJECT:' tag!) It is a shortening of "information" - as in 'for information'. Additional addressees, in other words.
Update: I note that this error is parroted from the Wikileaks "explanation":
The middle box contains the header information that is associated with the cable. It includes information about the receiver(s) as well as a general subject.although that may be referring to the three-letter "Subject Indicator Codes", which are not the same as the info addressees. Doesn't exonerate the Beeb in the slightest, however.