Interpret zsh bindkey escaped sequences
If speaking of a typical unix/linux flow of events the picture is roughly the following.
The terminal emulator program recieves the X events such as so and so button pressed, another button is released. Those events can be tracked with xev utility, for example. The terminal emulator then translates those events into escape sequences.
This translation is not set in stone. It can be configured. Different terminal emulators are configured differently. For example xterm translation can be set up in .Xdefaults like that:
XTerm*VT100*Translations:#override \
Ctrl<Key>Left: string(0x1B) string(OD) \n\
Ctrl<Key>Right: string(0x1B) string(OC) \n\
Note 0x1B which is ESC. ESC is also printed as ^[.
Now, zsh uses zle (and bash uses readline library for the same purpose) which interprets some of the sequences to move around the input line and perform editing actions.
The following texts should provide more additional details.
Zsh Line editor description
Wikipedia article on escape sequences
and
Xterm Control Sequences