It looks like that Google is not only indexing the pictures they find on the internet, they also apply some OCR on it.
I recently accidentally typed the serial number of one of my NAS drives into google image search, and it found the screenshot of one of my blog posts of it.
I still get some mild scary feelings when I see how capable Google is at indexing and making everything searchable that they can get a grasp on. It’s super handy and convenient but sometimes also a little bit scary.
I removed the original blog post during the migration, because I was unhappy about some parts of it.