On the Update Request email, there is a big "Update Form" button. There is also a hyperlink in tiny type at the bottom of the email that the user can click to "Go to the sheet".
It seems the "Go to the sheet" functionality is more likely to be the desired usage of the Update Request email than to launch a web form.
Could Smartsheet please move the tiny hyperlink to a more prominent place (perhaps another button?) within the body of the email?