Here's a link to the document explaining how NY interprets "convenience of the employer":
https://www.tax.ny.gov/pdf/memos/income/m06_5i.pdf
The document is from 2006, but I can't find any more recent updates (if any exist).
I tend to agree with @Hal_Al that your income is taxable by NY. Sounds like working from home was your preference and your employer did not object. Just my opinion.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
