Yes, I know it is 100% from a scammer. Although I do get emails from some of the gambling sites about withdrawal requests and all I have never gotten any sort of promotional emails from them. They would rather send it to your account in the gambling website. And it is easy to see in the notification section.
Withdrawal email is normal. But if you do not want to get the email again, you can go for the 2FA on the gambling site. Many gambling sites on this forum has 2FA feature.
My key takeaway from here is to have a dedicated email for gambling related activities. I use more than one emails for different gambling sites and it is difficult to tracked where issues like this originates from.
The reason I am using just one email is because I do not save my gambling site account password anywhere. I only click on forgot password to set another password and access the gambling site if I have forgotten the password. Having different emails for each gambling site will make this difficult.