Oh, I worked with them for two years in Nepal in the mid 1970s. It's possible things have changed since those days. Wooden isn't a term I'd use, not by a long shot, although I guess it depends what he meant by that. They're quick enough to show emotions when it suits. On parade, yep, they've got emotionlessness down pat.
Because of the poor educational facilities in the hill villages, many of them don't have the basic technical skills we take for granted from an early age, and there's a lot of catch-up involved. They're also not a great choice for peacekeeping activities, for any number of reasons. Loyalty and bravery are a given with them; this means that they can have difficulty getting their head around the idea that others might not be so honourable, or have a different sense of priorities. They're not an ideal choice, for example, for a fighting withdrawal. Going forward, or holding tight (which rarely involves staying put, but that's a digression), no-one can better them. Pulling back, not so much.
There can also be communication difficulties. A rumour does the rounds, which I've no way of proving or disproving either way, but it wouldn't be out of character. Down in the Falklands, a group were tasked with looking after some Argentine prisoners. Rumour has it that the instruction they were given was: "Take care of the prisoners", which - so the story goes - they misinterpreted.