The initial part of the question should go as follows:
"There are three components that are connected to form a system. Since the components in the 2–3 subsystem are connected in parallel, that subsystem will function if at least one of the two individual components functions. In order for the entire system to function, component 1 must function, as well as the 2–3 subsystem. The experiment consists of determining the condition of each component [S(success) for a functioning component and F(failure) for a non-functioning component]."
The question asked is referring to an event B where there are at least two functioning components of the system. In this case:
B = {SSS,SSF,SFS,FSS}
The answer contains every possibility where there are at least two functioning components. The first outcome may appear different than the rest as it contains three functioning components. However, event B says there are at least two functioning components but does not say there can only be two functioning components.