Although I doubt that every hit is for a key file that shouldn't be exposed (rather than a bug report mentioning it, or a code comment, or even a slice of code that looks for that line as a sanity check or similar, not to mention test keys and examples), it's still a stupid thing to upload if you are working on software.
And, as the blog points out, it's called a PRIVATE key in several places for a very good reason. Hell, most software that utilises them (SSH and Apache for a start, I believe) won't let you have them with certain UNIX permissions on the file because they KNOW how stupid that is to do and they'll just refuse to continue.
It is very interesting, though, what a well-crafted search can do. This is why I never listen to the "oh, no-one will ever know it's there but me" arguments that some admins try to use. They don't need to KNOW it's there. They just need to go looking for things that they know are interesting and the computer will help them find it. I've seen any amount of "private" website administration URL's in the past that were explicitly listed in robots.txt - they were bright enough to know that someone might find their secret area, but too stupid to realise that robots.txt would point you STRAIGHT AT IT if you were querying directly. Of course, the real security thing to do is just not have those folders accessible, which solves all your problems immediately. You can't stumble across a folder that doesn't exist, or is hidden behind a PROPER access control.
If you have something that needs securing, secure it.
This is also the reason I hate any and all "indexing" of documents or files. I don't CARE how well you think you've designed the system and encrypted the indices and whatever else. There's no reason to run through my documents folders and even network shares, and record details of everything in there. A file search through a folder is rare enough, and quick enough with modern hardware, that I don't even need an index to find anything I want within a reasonable time and - done properly - does NOT leave traces of even the searches I performed, or the documents I have, on my user account.
"Oh, look, the administrator's private account with no privileges just searched for a file on the network called X..." - Guess what the next target they will look for is - EVEN if you only use administrator accounts for the absolute minimum where they are necessary - all that does is raise the probability of that file being "interesting" to someone.