I think the author was referring to this in the context of improv, not normal conversation. It's bad to do in improv because it contributes nothing to the sketch - it's lazy and puts the entire effort onto the other person. It's much easier to riff off any kind of declarative statement or directed question. For example, "Dude this dog birthday is the weirdest party ever." or "So are you going to forgive my mom for dinner?" gives the other person an immediate context and hook to work with. Keegan-Michael Key explained this very well in a video on YouTube: https://www.youtube.com/watch?v=coZARWbdNls