The next line from your clip seems really relevant to this topic
when the invention was conceived or “reduced to practice” (actually created or a patent application filed) it related to the employer’s business or actual or “demonstrably anticipated” research or development, or...
In other words, if it's related to the employer's business it belongs to them. What's related and what is not is up to a judge to decide. There's arguably a spectrum of directly related, somewhat related, tangentially related, unrelated, etc.. Seems like the OP's project though is in the directly related side of the spectrum.
when the invention was conceived or “reduced to practice” (actually created or a patent application filed) it related to the employer’s business or actual or “demonstrably anticipated” research or development, or...
In other words, if it's related to the employer's business it belongs to them. What's related and what is not is up to a judge to decide. There's arguably a spectrum of directly related, somewhat related, tangentially related, unrelated, etc.. Seems like the OP's project though is in the directly related side of the spectrum.