i think this is the correct interpretation.
if you’ve got a really long torso, prefer the sleeve to hit closer to the elbow (rather than further up the arm), just like wearing more baggy clothing, or are afraid that your shirt will shrink a lot in a clothes dryer, then you could try sizing up.
there were comments in the “iNat hat” thread that some of the women’s shirts from the previous store were a bug snug across the bust, if i remember correctly, but don’t remember any comments saying that shirts from the current store fit unexpectedly.