How did you get to that conclusion?
It simply means that some people zapped, but never got zapped back. 🫤
If you're one of them, say hi, I ll fix this 🫡
Discussion
It could mean multiple things, including what you said. Any lightning wallet can pay a zap invoice. Only NIP-57 wallets can return the zap note that tells Nostr it was paid. So there could be 10000 zap receivers but 4000 use wallets that don’t support zaps and those paid invoices wouldn’t be registered as zaps on Nostr because their wallet doesn’t publish a zap note upon payment.