Login: "not a WordPress site" error sometimes displays incorrectly

Expected behavior

If I enter the URL for a WordPress site that blocks the app's requests for any reason, I expect to receive a helpful error message that informs me why I'm not able to log into that site via the app.

Actual behavior

Recent app reviews at pbArwn-4xZ-p2 clued us into the fact that there are some scenarios in which the following error displays when users attempt to log into self-hosted WordPress sites:

"The site at this address is not a WordPress site. For us to connect to it, the site must use WordPress."

For example, the user in 5170539-zd-woothemes was seeing the above error even though there site is using WordPress, but was blocked due to an inability to connect via cURL.

Screenshot:

Previous related issues:

• https://github.com/wordpress-mobile/WordPress-Android/issues/8459
• https://github.com/wordpress-mobile/WordPress-Android/issues/12401
• iOS version: https://github.com/wordpress-mobile/WordPress-iOS/issues/18497

Steps to reproduce the behavior

A URL for testing can be found at pbArwn-4xZ-p2#comment-5712 and/or 5170539-zd-woothemes (not included in this ticket to protect user privacy):

1. Navigate to the app's login screen and select the "Log in by entering site address" option.
2. Submit the test URL.

Note, more work needs to be done to identify the exact issues a site must have to reproduce this error, as disabling XML-RPC isn't enough to reproduce.

Tested on Pixel 6, Android 12, WPAndroid 19.7

Start at the login screen's site-address flow and reproduce the issue with the referenced test URL or support cases. Trace how blocked connections and non-WordPress responses become the displayed error, then verify that connection failures receive a helpful explanation without misidentifying the site.