What just happened on my phone?

(excuse my english) so i was scrolling through instagram, browsing memes as usual, when suddenly a pop up appears only for a brief second and all i could read was "screen recording" there were two choices to pick from but i can't remember if they were literally just empty boxes or not since the pop up disappeared really fast, like after a second or so. I hadnt clicked on anything weird, all i did was scroll. Is this a hidden feature or a glitch or what? I have an iphone 6s, if that helps. Am i just being dumb?

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