My phone screen cracked without being dropped

So i recently moved from my iPhone XR to my Dad’s perfect condition iPhone 11 Pro Max, I’ve had it a bit over a month now and I’ve tried my hardest not to damage anything on it. But last night i was going out for a cigarette and before i went out the phone was perfectly fine, i came back inside after keeping it in my hand the whole time no dropping, and it had a massive crack on it that i realised after getting a snapchat that revealed the spider web crack. This crack starts on the speaker left corner at the top of my phone and goes all over the place. Yet my case is perfectly clean and untouched. I’m kinda scared cus my parents are mad people and to have a phone for this long of time and already have damage that i don’t understand where its from it kinda annoying