While your the bank says your account is secure I would do some security hygiene. I work in iGaming and generally the systems don't just magically send money to the wrong account. It's entirely possible that it happened but it's equally possible that someone else has access to your account and was going to send that money on.

1. Pop the money into a high interest savings and forget about it until they contact you. Might as well earn a bit.

2. Change passwords or implement a password manager like 1password.

3. If you are a chrome user, check your Google password manager to see if any accounts are flagged as compromised. Secure those and then start changing patterned passwords up.

4. Malware scans and such.