Hi, Emily (not Emily from Reddit, are you?). What you’re missing is that although it’s true they can’t both be on the JUNIOR varsity, nothing about the rule says that they can’t both be on varsity. Imagine this partial layout:
Varsity: Tim, Wilma.
Now consider the rule: “If Tim is selected for junior varsity, then…”
Well, Tim ISN’T selected for junior varsity; therefore, the rule doesn’t apply to this situation.
A good general rule is that a single conditional rule (not an “if and only if” rule” cannot control all possible outcomes. In other words, by itself, one conditional can’t force two variables to the same side, or keep them separated.
Hope this helps.