In this situation, what is different between "What have you guys been up to?" and "What did you guys do?"?
"What have you guys been up to?" means "what have you guys been doing recently?" Therefore, this is an open question where the response can be anything. On the other hand, "what did you guys do?" is inquiring about one specific activity. Ex: A: What have you been up to today? B: Today I had lunch, went shopping, and saw a movie. Ex: A: I heard you went to the zoo yesterday. What did you do? B: I saw the elephants and giraffes.