M4A music files working fine on Galaxy S5?

I've heard of people having problems playing.m4a files on Android and how they shouldn't work on an Android because.m4a is built for iTunes/iPhone. I added MPEG4 songs onto my GS5 and they are showing up on my phone as.m4a files. It was a direct copy and paste. When I copied it, it asked if I wanted to convert it to wma or the phone might not able able to play it but I clicked "just copy" so they are pure m4a files playing perfectly on Android. How am I doing this if it's known to be an Apple file and people seemingly can't play them on Android with downloading another music playing app? Yes, I am using the standard music app that comes with the phone.
Added (1). NOTE: The m4a songs did not come from iTunes. They were downloaded off some random music sharing site.

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