I think that while Sterlo may have been a Manly fan when he was a kid, he looks at some of the players in our team (Jorge, Wolfman and Horo) and is a bit envious about what they are doing in the maroon & white and that they aren't doing it at Parramatta.
I remember him saying (with a laugh) when Beaver scored his try in the 2008 GF that "Parramatta tried to sign him early in his career but he stayed where he was.....what a shame" or words to that effect.
In all honesty though, while no doubt he would prefer it to be Parramatta winning, I think Sterlo genuinely just loves a good game of rugby league no matter who is playing.