drupal error message "The form has become outdated. Copy any unsaved work in the form below and then reload this page"

Steps to reproduce the bug?
1) log in as a auth user (not admin)
2) click on any node's "add comment"
3) insert any dummy text.
4) take few moments before clicking "save" then click "save" button

The behavior I was expecting?
To just save the comment

What happened instead?
The result is an error "
"The form has become outdated. Copy any unsaved work in the form below and then reload this page"

I got into an argument with my developer. He thinks this is a normal security behavior that Drupal core does on all sites. I think this is unacceptable behavior due to the fact that I do not expect my site users to be computer savvy. I don't expect people to copy their comment then click "reload" then paste it again then click "save" again.
What you think and what is the solution. I have been researching but i couldn't find this error except with sites that has some multi-form function.
Please see the image attached. .