Regardless of which network they connect from, I would expect that a network engineer knows that if a TCP handshake with the web server (i.e. after DNS lookup)

Regardless of which network they connect from, I would expect that a network engineer knows that if a TCP handshake with the web server (i.e. after DNS lookup) fails at the 3rd step, then it's not DNS. The fact that the TCP handshake begun is evidence that DNS works.