The complaint isn't that an email address was asked for, it's that the ask didn't happen up front. Having someone spend time doing something and then asking for an email address before giving the results is the Bad Thing here.
I don't think the author would have complained if the email address was asked for prior to him starting to actually use the service.
It's like I install a brand new text editor software, spent some time to write a story, and when click on the "save" option, it asking for the payment - that's dishonest and shows that there can be more such dishonest behaviors in the future. But if the same software asked me for a payment upfront, that's totally understandable. Or, if it said upfront that "this is a limited demo, you can save documents up to 150 words, and if you have to save larger documents, you need to pay", that's being very straightforward to the users.