The bug in 4.0.0 is this which was fixed in 4.0.1. It had nothing to do with the entropy bug that already existed in 4.0.0
// 4.0.0
bool ckcc_vcp_enabled = true;
// 4.0.1
bool ckcc_vcp_enabled; // defaults false
My understanding is the bug was introduced in 4.0.0
The confusion comes from the fact that since they patched a bug in that version, they removed it from the list of releases instead of keeping it and adding a "THIS IS A VULNERABLE VERSION" disclaimer.
Therefore people see that the first version released after 3.x.x was 4.0.1 and assume that this was where the bug was introduced.