The search area given by The Telegraph would make sense if it was established that the unidentified radar contact heading west was not picked up by Indian primary radar on the Andamans or Nicobars. The logical thing would be to comb that radar coverage gap in the middle with no primary radar coverage from either side.
If the "UFO" diverted to the SW (direction Diego Garcia) in that potential radar gap nobody would have noticed. Such a hypothetical diversion would bring into play the Pentagon. In Diego Garcia there must be some impressive surveillance equipment, AWACS and the like. Maybe something was picked up there ?