Yes, it is taxable income for you. Your employer could issue you a Form 1099-MISC, and put the income amount in the box 3, Other income, or Form 1099-NEC, non-employee compensation. However, he couldn't classify that income as rent, that was a mistake.
You can report it as Other Income. Follow these steps to enter it in TurboTax:
Federal Taxes -> Wages & Income -> I'll choose what I work on -> Scroll to the bottom and under Less Common Income select Start (or Update) for Miscellaneous Income. You can enter your 1099-MISC information there.
