Is z-axis zero near the hotend?
Generally, Z-axis zero is when the hot end and the build plate are close to each other.  Some printers keep the hot end up at the top, and bring the build plate up to reach it.  Other printers keep the build plate at the bottom, and lower the hot end down to reach it.  As such, "Z axis zero" doesn't specify top or bottom of the physical printer, it just specifies that the hot end is right up against the build plate, ready to print its first layer.  In the printer you describe, where the hot end remains at the top, that's where Z zero is.

In terms of the model being printed, Z axis zero is always the bottom of the model, the first layer to be deposited on the build plate.  The numbers increase from there, either lifting the hot end up, or pushing the build plate down, depending on the design of the printer.