I was mildly surprised when my university supplies office offered to sell some liquid nitrogen to me, no questions asked. Which was disconcerting for few reasons: I asked for dry ice, I lacked a dewar, and I would have to transport it on a subway. All they knew was that I was collecting supplies for a science demo. Granted, a demo using liquid nitrogen would be much more fun. It simply wasn't an option on short notice.
A thermos works fine. Safer if pretty underfilled. I'm not surprised by the response, to people who work with it regularly it's not a big deal. It's not like they were offering it to kid. That you knew enough to find it concerning is good enough. :)
