Confusing smart list business rule syntax

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Somehow the example below is valid syntax but I don't know why.  In addition in my simple example the "IF" condition is only satisfied when Project Type == SL_ProjectType.Option2 but not when equal to Option1 which is confusing.  Can someone shed some light on using multiple smart list references on the right side of an ==?

 

IF("Project Type" == [[SL_ProjectType.Option1,SL_ProjectType.Option2]])

     do something;

ENDIF