Alexa sees a link as backlink to my website which I attached on Upwork inbox.(?)

[khayal]

When I check the backlinks for my website on Alexa, I noticed that , there's a backlink from Upwork, and when I clicked that link, I realized that it's the link of my Upwork inbox and I entered my login credentials to access that page.

My question is : How it is possible for Alexa to get that link which I need to enter my details to access the page?

[Mobilio]

Alexa uses toolbar installed to users computer to scan for links and sent them to their cloud as "backlinks". There isn't way to index someone other inbox folder for links as far as i know.

I have installed on mine site Linkstant and here is similar "backlinks":
http://mail2.daum.net/hanmailex/Top.daum (this is korean mail)
http://www.notprovided.eu/wp-admin/edit-comments.php (heh, seems that someone visit mine website just to check is comment legit or don't) http://foreman2.cnet.com:9058/rb-foreman/flows.html?_flowId=edit-item-flow&id=75852664&versionCnt=0 (ups, i don't have access to this server)
http://www.reddit.com/message/unread/ (reddit inbox)
http://mail.naver.com/?n=1415975274556 (another mailbox)
http://1.1.1.1/login.html (probably internal network)

So LinkStant show this as inbound links to me in their report and i'm almost 99% sure that there IS links somewhere. Same happens with Alexa - he detect links and upload them to their reporting engine. And this engine count link as legit.