macOS app rejected for Thumbnail extension continuing to run

I received a rejection for "Your app spawns processes that continue running after the user has quit the app."

The process in question is the app's Thumbnail extension.

When I remove all of my own code from the thumbnail extension, it still continues to run after I exit my app. This is the entirety of the extension's code, which now renders blank thumbnails:

import QuickLookThumbnailing

class ThumbnailProvider: QLThumbnailProvider {

    override init() { }

    override func provideThumbnail(for request: QLFileThumbnailRequest,
                                   _ handler: @escaping (QLThumbnailReply?, Error?) -> Void) {

        let reply = QLThumbnailReply(contextSize: request.maximumSize) { (context: CGContext) -> Bool in
            return true
        }

        handler(reply, nil)
    }

}

Presumably Thumbnail extensions continue to run so that Finder (among others) can generate thumbnails as necessary. AFAIK, I have no direct control over the extension's lifecycle.

Is this just App Review's mistake? The "Next Steps" are clueless:

"You can resolve this by leaving this option unchecked by default, providing the user the option to turn it on."

The app uses its own thumbnail extension to render thumbnails for document templates, which may be an uncommon thing.