I received a W-2 from my employer as well as a W-2 and 1099 Misc from their insurance company (Guardian) for MAFML for maternity leave. Why not a 1099 G?

The form 1099G is for a government payment.  MA employers can choose the state plan or a private plan.  The private plan payments can be on a form 1099-Misc.  The form 1099-Misc does not necessarily indicate self-employment.  The amount reported in box 3 is "Other Income."  

Enter the form in the "Wages & Income" section.  Scroll to "Other Common Income" and select the 1099-Misc topic.  Enter the form information and answer that the pay "did not involve work."