Frontend & browser·Loading, assets and the critical path
you opened the connection to the image host early so the first request did not pay for DNS and TLS.
Preconnect
Also calledrel=preconnect, dns-prefetch
A hint to complete DNS resolution, the TCP handshake and the TLS negotiation for an origin before anything is requested from it. On a cross-origin critical resource that saves a hundred milliseconds or more of pure setup. Connections are held open only briefly and each one costs the client and server real resources, so it is worth doing for two or three origins and counterproductive for ten.