Faraday Bag and USB charger question

Recently I attended a security conference where the speaker was talking about the effectiveness of the faraday bags. The speaker said that something that raised my eyebrow. He said that if you put your phone in a faraday bag while you got a usb charging cable coming out of it because you want to charge it at the same time, the charging cable becomes an antenna. How does that work? I thought USB cable is designed to shield itself from …

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