This is incorrect. As Mark Roberts pointed out:
Furthermore, the object tracked by radar was most definitely not moving at supersonic speeds. On top of that, post-crash debris was that of a jet, not a missile. Furthermore, no missile carries humans; corpses of passengers known to have been on Flight 77 were found in the debris, still strapped to their seats.
On top of that, FL77 was indeed witness by another airplane, with the pilot testifying to what he saw.
911thology's claim is not only presented here with zero supporting evidence (in other words, he merely states the claiim, he provides no proof for his statement), but is contradicted by the weight of the evidence that has been recovered.
Flight path study:
http://www.ntsb.gov/info/foia_fri.htm
Pentagon witness statements:
http://sites.google.com/site/wtc7lies/PentWitnesses.xls
Mark Roberts' collection of links to evidnece:
Summary of evidence:
http://sites.google.com/site/wtc7lies/911pentagonflight77evidencesummary
This claim is demonstrably untrue.