Anybody knows what strange phenomenon is this??

I was having lunch and scrolling through Facebook in my primary phone when the screen just went like this. Completely still and wierd sound for a second. Caught me by surpise before I managed to take a picture in my work phone. Waited for a minute and pressed the power button for a few seconds untill it switched off and now phone's back to normal. It's a Motorola g54. Been only a year since I bought it. This hasn't happened before Does anyone know why this happened and should I be worried cocos?? It isn't paranormal activities right??