I just read that https://support.apple.com/en-us/HT204413 updates the kernel file, and forgets to set the hidden flag, leaving a 'strange file on my hard drive' that a user may elect to trash. (Bad Idea)

Anyone care to confirm this? I haven't ran that here yet.

What is the path to that file?

/mach_kernel

I ran the update and I don't see that file.

I too ran that update and don't see the file either.

I haven't had the issue either but here is a site https://support.apple.com/en-us/HT203829 This file is installed with OS X and should not be deleted. In some cases, it may be visible in the Finder. The file can be hidden again using the following steps.
1 Login as an Admin user.
2 Open Terminal (located in /Applications/Utilities).
3 Enter the following command, then press the return key:
4 sudo chflags hidden /mach_kernel
5 Enter an Admin password at the "Password:" prompt.
6 Quit Terminal.
This may prove useful for some with the issue

The visible kernel file did occur on an earlier version of OS X, perhaps on one of the 10.9.x updates. I haven't seen it with 10.10.x.