The chances of writing the same words is impossible, but the chances of writing the same idea in similar ways is very possible. If the later happens, it may look like paraphrasing.
Moreso, I pointed out that people overtime tends to confuse their original words and/or ideas from adopted ones. This happens to especially great readers, in order to be very sure, it wouldn't cost much to run a plagiarism test before publishing.
Got a point but even there is a chance someone is paraphrasing an idea from others, this could be very hard to detect as plagiarism cause the description of it states about using others content in a disgrace manner without having reference source or what.
Maybe you are right, it only took a small time to run it. But this isnt necessary at all for natural writers. Maybe for writers they used this but for someone that is just a normal person I doubt they would mind.