The two translations come from the two meanings of 그래(요). 1. 그래 as short for 그러해 (그러하다 in the -아/어 ending). It's an adjective meaning it/something is so, or "like that". So its question form 그래? means "Is that so?", which is about the same as "Really?". 2. 그래 as short for 그리해 (from 그리하다 - note 리, not 러), which means 그렇게 하다. It means to do so / that. There are two cases for this meaning, because the -해 ending acts both imperative and declarative. A: Imperative. 그래 in this case means "(Yes / Okay), do so/that" - it typically gives a permission, like :okay", to someone asking whether it's okay to do something (그러세요 is its more polite version). B: Declarative. 그래 describes someone's action. This is quite similar to the adjective case (1 above), but it's grammatically distinguished. For example, 1. A: 저 이번에 취직했어요. B: 그래요? 잘됐네요. (Is that right? [Really?] That's great) == (equivalent to) 그렇습니까? 2(A). A: 저는 먼저 가 보겠습니다. 네, 그래요 [그러세요]. (Okay, go ahead) == 그러십시오. 2(B). (to someone acting in a strange way) 왜 그래요? [그러세요?] (Why are you acting like that?) == 그러십니까?

it can mean both it just depends on the situation