Deleting the Google account alone isn't likely to erase anything on the phone besides logging out of Google related apps. Someone else wouldn't be able to get into gmail, for instance, but would still have access to files stored on the phone (if there wasn't a screen lock) and SD card.
If I'm understanding correctly, you had files in a password protected folder plus did a remote wipe before deleting the Google account. "Secure folders" may or may not be truly secure, depending on the app used to control it. A lot of third party apps only do something like rename the files and put them in a hidden folder but don't actually encrypt them. That would take about two seconds for a hacker to find. Since you did the remote wipe, I still wouldn't worry, as that would not only erase the phone but also enable factory reset protection.
Deleting your Google account was likely overkill, as FRP wouldn't allow anyone to access the phone until your Google account info was entered during the next setup to verify ownership of the phone. And if that wasn't enough, phones today have their internal storage encrypted by default, so there would be no recoverable data even if FRP was not enabled.
As you may have guessed by now, there's a down side to deleting your account. If you happen to find your phone again and FRP is enabled, it may not let you back into it due to not having an account anymore. That's not a situation I've seen addressed before, but hopefully one of the other members can fill us in on your options in this situation.