No, the income you earned while living in PA should not be MA-sourced, even if it was for an MA company.
MA did have a rule in place until September 13, 2021 that stated if you were telecommuting from out-of-state due to a pandemic-related circumstance then that income is taxable by Massachusetts. However, you have already stated that you were not telecommuting because of the pandemic. Therefore, your employer was correct in withholding PA taxes and those are the only taxes you should pay while you were telecommuting.
