The number 2 Pencil story

In the 2ed grade ,I saw my friend chewing on
his number 2 pencil,, then he asked to use the Bathroom
the teacher asked ,is it a number two ,or can you wait
For years I thought that’s where the expression
A number 2 came from
Then I found out it really came from when
lead removed from pencils to graphite
getting the lead out ,,,,moving Fast