@traceymoko: Thanks! Yep this solved the visible part of it at least, the email address is no longer displayed on the /about page.
Although when I view source in my browser, and look and the HTML given to the browser, it still has the current contact email address in the HTML inside a <div class="hidden" id="data-preloaded" data-preloaded=...> tag such as \"contact_email\":\"currentadminemail@example.com\",
A bit strange. And I guess that spambot scraping the pages are still going to get the email address exactly the same way.
I even tried changing the email address to a different one, but it does serve whatever the current email address is, i.e. it’s not a caching issue.