Question about interrupt0

Hi, I have a question about interrupt0 in the hardware level.
I am using a Arduino Mega 2560 board(v2). I know external interrupt 0 is linked to pin2. However, from the schematic, it seems that pin2 is linked to interrupt 4.
Here is part of the schematic:

I want to know why it is interrupt 4 in the schematic and interrupt 0 in fact?
Any help will be appreciated. Thank you in advance.

I believe it is a throwback to the Uno. On an Arduino Uno, interrupt 0 is connected to pin 2, so pin2 is called external Int 0. On a Mega they needed to still have an interrupt pin connected to pin 2. It just so happened that they chose INT4.

Thank you. It sounds reasonable.