A learning curve is a plot of work required for achieving some amount of learning. Those guys just didn't get that that was how it's being used.

"How hard is it to learn Haskell?" Not "How much time does it take to learn Haskell?"

For instance, people will say some things are easy to learn, hard to master (playing Go). Other things are hard to learn but once you have, you're close to mastering them (kinds of problems that have a trick - like integrating e^ax cos bx).

Considering that he says it "pushed him", I'd guess he means that there was a lot to learn and it didn't come easy.