Due to this uncertainty, I'm not about to enter my twitter credentials. Just seems too risky.
"In the next page you will be able to share it with your friends on Twitter, Facebook etc"
What is "it"? What is being shared?
it just posts a link to the list page you have just created saying.. "I am looking for tweeters to follow for the topic X. please contribute" along with a link to the page.
it posts into your twitter timeline and not to anyone else directly.
if you want to word it yourself, you can post it by unchecking the option to post automatically. I guess this communication is not clear. I will work on it. Thanks for bringing this to light. Please do try it. You can even try it without logging in.