The elonjet tracker posts those locations after a delay of a few hours. If someone wanted to use its posts to hunt him down, they'd always be behind the curve. At least that's what their Twitter account does.
As a few others have already mentioned, the plane's flight information is public. If someone was really interested in stalking him, they can see near-real-time information on one of those plane tracker sites.
Anyway, that's not really a Nostr issue, as the exact same info gets posted to Twitter and the Fediverse.