Sony ARWs Opening With Unknown Preset

All raw files you view in Adobe products, regardless of the version of Camera Raw, or the camera model, have an Adobe rendering according to the Adobe factory default or a default you may have set, which will be different than the camera rendering, sometimes not much difference, sometimes quite a bit of difference.  FastStone will show you the camera-embedded JPG which is also what you see on the camera's preview display and you will only see this momentarily in Adobe products before the Adobe rendering is computed and a preview created.

When you say there is a preset being applied, is that another way of saying Adobe rendering is different than camera rendering--which it will always be to some degree, or do you mean that there are non-zero settings in the Basic Toning tab, the area where you adjust Brightness and Shadows, and Clarity and such? 

In either case, you can set a new default by opening a brand new image that you hvaen't made any purposeful adjustments to, then make only the adjustments you want to have all photos from that camera to start with.  Usually you set things like enabling lens profile corrections, a default level of noise reduction, and the color profile you want to start each photo with: Adobe Color, Adobe Neutral, Camera Neutral, etc, depending on the specific list your camera has.  Once you have made the handful of adjustments that you'd like every photo to start with (from that camera), press the Alt or Opt key and a button will set Set Defaults... and you click that to save the current settings as the new default for new photos you open for the first time.

There is a problem with the newest Sony model in that Adobe cannot decode some of the information in the raw file and has to guess how to render the files.  What specific Sony model camera are you working with?

I guess it's just the Adobe Color profile being added, but it's real bad for the a7R III. The Neutral profile for the camera is better, but it's not great either...