Having just completed a book about round-the-world voyages of scientists and explorers from the 1760s, and having traveled to only a tiny fraction of the locations portrayed in the book, I feel compelled to agree with him.
Yet there's a crucial caveat that goes unuttered by Englander too. Consider "Shakespeare" vs. Ben Jonson. Now, for instance, Jonson sets Volpone in Venice, and Jonson never traveled there.
But as one Jonson scholar noted, "Romeo and Juliet is part of an Italian night [!]; Shylock would possibly be ill at ease away from the Rialto[!!]; but the scene of [Volpone] might as well have been laid in Madrid or Edinburgh for all the effect Venice has on the characters."
In other words, Volpone is a great play -- just not a great Venetian play.
"Shakespeare," on the other hand... well, the Jonson scholar above isn't just making idle chatter. SBAN and Richard Roe's Shakespeare's Guide to Italy are just two of a number of books over the years that concur with the Jonson scholar and make it clear how much personal experience of the author's own Italian travels went into R&J, Merchant of Venice, etc.
So I certainly agree with Englander that writers should of course feel free to venture far and wide in the places and historical timeframes they write about. But there's still no faking first-hand knowledge.
In that sense, pace Mr. Englander, "Write what you know" really requires no interpretation at all. Nothing more or less than... "Write what you know."