Why are we supposed to imply that the only reason leonard and the guys met penny is because she moved in across the hall?

One of the episodes of Big bang, they show leonard looking across the hall (i think it was the first episode in fact), and seeing this tall blonde bombshell. He gets up the nerve to just go say hi, but, that doesn't mean she HAD to befriend him and the guys. What would have happened if she had moved in to an apartment on a lower or higher level. Would they still have become friends? I mean, is placement really that big of a factor in how and when you meet someone?

Why are we supposed to imply that the only reason leonard and the guys met penny is because she moved in across the hall?
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