Looks to me like he's suggesting that this character is holding his hands up in that half-shrugging "I don't know nothin'!" kind of way
Forgive the meme but this is the only picture that popped up in my 15 seconds of intense google imaging:
Whether or not this is 外国人のくせ I don't know, but that's what came to mind for me. Reading over it again I don't think the emotional quality of it is the same but I think the general gesture could be the same.
Either that or the author has his own idea of how foreigners act.
Edit: I'd like to comment that Chocolate's suggestion (from the position of a native speaker) of a pure shrug may be accurate here, although apparently none of us as foreigners immediately associate shrugging with raising of the hands as much as we do with shoulders. However Japanese does have the word 肩をすくめる to refer to shrugging the shoulders. Seems to be a distinction between which way the palms are facing!
Either way the following image describes my feelings adequately.