No, for this specific situation not. A CSRF attack allows an attacker to exploit the rights that a victim has,
e.g. bank.com/pay?ammount=1000&to=34.67.978.246
It makes no sense to attack the log in form, since an attacker can log in by himself if he has the information that is required for a succesfull attack on the login field (the username and password).
The reason why Rails uses CSRF protection on the login field is simple: it’s much more simple to implement CSRF protection globally than for 95% of the fields 😉