A web server can be configured to send a default ssl cert if the browser does not support SNI, but can still route the request to the correct virtual host based on the HTTP Host: header if the customer clicks through the warning.
The following two https sites exist on the same IP:
grepular.com
emailprivacytester.com
If your browser doesn't support SNI, then the cert for "grepular.com" will be returned by default. So browsers which don't support SNI will not notice anything unusual when visiting https://grepular.com/, but will get the cert for grepular.com instead of emailprivacytester.com when visiting https://emailprivacytester.com/
Unless you have IPv6 support, in which case the sites have different IPs so SNI isn't required (exactly like cloudflare have just done)
The following two https sites exist on the same IP:
grepular.com emailprivacytester.com
If your browser doesn't support SNI, then the cert for "grepular.com" will be returned by default. So browsers which don't support SNI will not notice anything unusual when visiting https://grepular.com/, but will get the cert for grepular.com instead of emailprivacytester.com when visiting https://emailprivacytester.com/
Unless you have IPv6 support, in which case the sites have different IPs so SNI isn't required (exactly like cloudflare have just done)