Is Google responsible for th1s_1s_a_4o4.html?

Found this on a Site Lock Facebook page.

SiteLock - Website Security Thanks for the info. After looking into your account, you do have a free scanner provided by your hosting company. In order for us to verify that your 404 page is clean, we actually try to provoke a 404 error by making a request to a non-existent page (e.g. th1s_1s_a_4o4.html). Please let us know if you have any further questions!

Whatever is hitting your site with that URL, it doesn't look like it is Google. I checked my server logs and none of my sites have had that URL requested in the past month. If it were Googlebot, I would expect theme to request such a URL on all sites they crawl.

https://productforums.google.com/forum/#!topic/webmasters/MkfVFWOTl5I has a user agent from such a hit: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/6.0)" which isn't a user agent that Googlebot would use.

A responder in that thread checks the client IP address and determined that it isn't an IP address that Google uses.

There is a clue there about why this is happening though. In the case in which it was posted there was a referral URL along with the request: http://www.google.com/url?url=www.<censored-spam-site>.ca&yahoo.com. It looks to me like this is a spammer that is trying to get traffic to their site by spamming your 404 report and referral report. They are using Google as a redirector to make the URL look more legitimate. Also appending yahoo to it just for good measure.

It is safe to ignore spam like this.