I moved this from the G3 forum to the More LG Phones forum (unfortunately, there's no Stylo 3 forum, although there are ones for the Stylo 2 and 4, go figure).
Those images are probably cached files used by some app. They might be related to an ad service, or sample images from an app. A good app developer knows to add a .nomedia file in the directory where the app caches images (since a .nomedia file in the directory instructs the system to ignore that directory when adding pictures to the gallery database), but unfortunately, there are many mediocre developers out there.
In your gallery app, select one of those images, then tap Information or Details, and see which directory the images are in. You could then use a file manager app to create a blank file titled .nomedia, and that should hide the directory from the gallery app.