You have done the right thing by contacting your bank immediately. Be sure to follow up with them regularly (weekly is very reasonable if you haven't heard from them on status), provide any paperwork promptly (filling a form claiming this was not an authorized payment, for instance), etc.
You will also want to talk with your bank about the potential to change account information. This will be down to risk of more such transactions vs inconvenience - if you have a lot of things tied to your bank account it might not be worth the trouble for a one time issue. But it is possible that you will want to, or the bank will recommend, closing/re-opening your account with new information (all new account number, cancel all attached cards, etc.).
For now, I would suggest you treat the account as "potentially compromised". Be in a position where if the account is closed tomorrow you will be OK, having money in another account, having cash, etc. Make sure you can make your housing payment (if you have one), pay for food and transportation for the month, etc. This is an "abundance of caution" approach, but it basically just means you are prepared for the worst-case scenario of being without that particular account/banking service for a few weeks. It should not be that disruptive to you, but good to be prepared.
As for identity theft, this is actually a perfect description of the problem inherent with identity theft - you are unlikely to have any way of knowing the cause or the source. There are so many leaks that it could have been related to Equifax, or it could be one of the other countless leaks that are known, or it could be part of a leak that is not yet known, or it could be something else entirely. There are so many possibilities!
Dealing with unauthorized payments is now the norm. It is part and parcel of financial life in our age now, and while you can try to minimize its likelihood of occurrence, I believe the better strategy now is to assume it will happen on occasion, perhaps at least once a year, and prepare accordingly. Don't rely on any one account to be 100% available and working 24/7, don't have all your money in one place, and make sure you review all your spending/transactions at least monthly (I find it is harder to remember what is what after a whole month, so weekly or bi-weekly may be easier for you). You don't have to do anything wrong for something like this to happen - it just happens now.