That's the problem with reported conversation - I suspect there was a smile on his face as he was saying that, and I for one was expecting an "(audience laughter)" at the end of the sentence.
True, Rob's jokes can be very dry and subtle. If he ever looks at the golang-nuts Google group [1] (which he evidently does) there's no way this couldn't have been sarcasm. Many questions from newbies touch on the topic of generics.
[1] https://groups.google.com/forum/?fromgroups#!forum/golang-nu...