Flush your DNS cache, and try your browser access again. As you're on OS X 10.13 or later, you can use the following Terminal.app command to flush your network caches:
sudo killall -HUP mDNSResponder
This command is benign, though it'll initially slow down some subsequent network accesses, until the DNS translations are re-retrieved and re-cached.
You'll have to use an admin password for the sudo.
Why? The web server is told which web site to display based on information accessed from and routed to and then sent over from your web browser client. If your local system has cached an old DNS entry or—as was mentioned earlier—the hosts file was modified, then the wrong IP address can be targeted or—and this detail is not applicable in this case, though this is how virtual hosting is implemented on the web server—the wrong host name can be sent over from the web client to the web server.
The Time To Live (TTL) for your DNS entry from your DNS provider is set to 19332, which means that translations will usually be maintained in a local cache for roughly five hours.
Another possibility here is that the Mac is using a different DNS provider than the other devices you're testing with, and the DNS provider that the Mac is using has not updated its translation caches.
When moving a web site around, it's common to lower the TTL values leading up to a server or address or network migration, and to then increase the values after the migration. This increases the load on the DNS servers and slows access traffic, but it makes for a quicker change-over when the new translations are available. Some folks will go as far as gradually lowering the TTL. Returning the TTL to a larger value after the network transition has completed speeds frequent user access, as the DNS translations can be cached for longer.
