Thanks for the post in Apple Support Communities. I see you have a question about Siri Search Suggestions.
Siri Suggestions can come up when using most of the apps on your device, and the suggestions are geared toward actions you might take frequently, like visiting a particular website. You can learn more about this, including how to turn these suggestions off, here: Use Siri Shortcuts.
A "top hit" would be based on your bookmarks and browsing history from Safari. This is a Mac-related article but the same principle applies: Customize searching in Safari on Mac. Any Google Suggestions would be based on Google search algorithms.
I hope I've answered your question.