Lets not be hasty, I don't think Graham has any hidden agendas with Yamato. On the contrary it could be Yamato giving wrong info to Graham but the info were dispensed in good faith. At this point, Yamato has not officially comfirmed the VF-0A Shin's arms are made from POMs or not, so lets not jump to conclusions.
Lets be patient for a bit more, lets see what Yamato has to say first.