That is an opinion,for which there is no proof : the German policy against Poland was the same as the one against CZ : bluffing and threatening to force CZ/Poland to accept its demands and to scare Britain . Only ,ONLY,if the threats did not work (September 1938/August 1939 ) would force be used :the decision to use force, depending on the possibility on a deal with Stalin, was made in August 1939, NOT in March : nothing special happened in March .
Polish diplomatic reports , diplomatic reports in general, do not give a correct report of the intentions/decisions of the opponent ,because, as all reports ,their contents are decided by what want their superiors : if the Foreign Office wants an alarmist report , they will have one .It is the same for the reports of the spy services : US secret services tell us that Russia will invade Ukraine,because Washington wants such messages .
Every one knew in March 1939 what Germany wanted , everyone knew this also in March 1933 and before .