I think there are two take-aways from this discussion:
(1) PHB's idioms, despite the mixed one, are quite widely-known in North American English. ('Screwed the pooch' may be a little less common, but I've barely seen a political discussion in years in Canada or the U.S. that didn't involve someone getting 'thrown under the bus'.)
(2) Despite being common to a relatively large region, they are nonetheless regional, and so widely *unknown* to those not native to North American English.
Which makes the comic particularly plausible - the idioms are not particularly esoteric, and not at all surprising that PHB would use them, yet with Asok's foreign charm not surprising that he might not pick up on them.
On a related note...only 4 stars? This is one of the few comics that literally made me laugh out loud when I hit the punchline.
I was talking to some coworkers in the USA about an issue and said, 'well there is more than one way to skin the cat.' Man they started laughing! They were not orginally from here I think but had been here a long long time and that idiom wsa not known to them... they thought I was crazzzy!
I feel compelled to explain the reference to the dog. Think of a dark room, a "significant other", and a case of mistaken identity. The expression originally meant to do something that seemed right at the time but that turned out to be terribly wrong. Now, it just means to make a serious mistake...