I can kind of see what he means, although I think the comparison with the uncanny valley is a bit weak.
I've taken to using Google Now's voice commands to set timers while I'm cooking, so something like "Ok Google, set a timer for 20 minutes". I don't have to touch my phone and it works brilliantly even in the noisy environments of a kitchen.
I've gotten used to talking to it in a very naturalistic way, which is where the problems occasionally crop up, and when they do they can be quite jarring.
A good example was the last time I asked it to set a timer for "an hour and a half", which Now interpreted as 1:00:30s, i.e. an hour and a half *minute*.
The jarring effect is at this edge where we feel like the speech recognition system is understanding what we say, but really it's just trying to use lots of different rules and patterns that have been coded in. If you happen to just fall outside of one of those rules it fails completely, and it can seem very arbitrary.