When you say it's rated at 47F do you mean its efficiency is measured at 47F? If so, does that matter much?
The unit linked in the post you're replying to states that it can operate as low as -13F.
The unit linked in the post you're replying to states that it can operate as low as -13F.
When heating, it pulls it from the outside air. As it gets colder, there is less heat to pull out. Typically heat pumps will still keep pulling heat at >100% efficiency nearly into the negatives, but the amount they're extracting isn't enough to keep up with the heat loss of the house.
Heat lost of the house is a factor of insulation, surface area and heat gradient. It's a lot harder to keep a house at 68F when it's 5F outside than it is when it is 50F.
So when it's cold out, you need more heat generation, and there's less heat to pull from the air. That's why heat pumps have backup auxiliary heat.