"It seems like it applies to folks who are nonresidents but do actually travel into MA to perform work. Is this understanding correct?"
Yes, that's correct. MA can tax nonresidents on income earned from work actually (physically) performed within the state of Massachusetts.
MA does not tax nonresidents on income earned remotely from a location outside the state.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
