This is because the “tty” (by which I mean the device named by the output of ´tty´) is only displaying what is sent to it. Be it from the keyboard or pty2.
The fact that the keyboard also fills an input buffer from python has to do with how python and the keyboard are attached to the same input file device which is a separate thing from them having same output file device.
If anything that could output to tty2 could inject inputs to something using tty2 as an input buffer, that would be a security nightmare.
Now, I’ll sit back and let Cunningham’s law kick in.