A toy reused nonce makes the same keystream appear twice.
Both records use the same nonce
Nonce A is 0x000000000001, and nonce B is the same pinned bytes.
nonce A=0x000000000001
The nonce bytes match
The helper requires nonce A and nonce B to match before it models a reused keystream.
nonce reused=1
The toy keystream is reused
With the same toy nonce, this example reuses keystream 0x0f1e2d3c4b5a.
keystream=0x0f1e2d3c4b5a
Summary
The problem starts before any clever math: the same nonce leads this toy to the same keystream.
byte length=6