Actually, when typing a wrong Atlassian URL in a web browser, there is only a message saying that "Your Atlassian Cloud site is currently unavailable. Please check Atlassian Status for known problems ..." There are no mean to know if the Atlassian URL is maybe wrong/doesn't exist.
Like reaching https://dfsdfwfwef.atlassian.net/, a message saying that this URL doesn't exist within Atlassian Cloud instead of "currently unavailable" could make sense and will be more friendly to customers informing that this site URL doesn't exist and inviting him to create this site or there is no needs to wait for its availability.