I have a Google Pixel 3 XL and it has been playing up all day. Basically looks like it is being used when I'm not touching it. Mostly the notification centre comes down all the time or it opens the clock app. Also, anytime I press the screen the notification centre comes down.
It is possible that this has occurred due to a cracked screen, however my nan dropped it back in November and I have not had any problems with the function of the device until now.
Because I have never broken or lost a phone before, I don't pay for insurance.
Do you think this issue is a warranty issue or will they attribute it to the physical damage on the screen even though it has worked perfectly until today?
It is very difficult to say without assessing it, you could, in theory, submit it for repair stating "it's not working" however this would be disingenuous and might bite you on the backside when they open it up and find the physical damage.
Just because something works perfectly now, does not mean that in X number of months it starts to fail because the contact that is now loose from the fall is getting further apart.
I'd agree with @Jeneral__Pain,
The symptoms to describe suggest something is not working with the screen. There are actually three screens in a phone - the display, the touch sensors and the protective outercase. It sounds like you may have damaged two of them.
You say the clock app opens. As a test move the clock widget to somewhere else and put some other widget where it is. See if those start opening.
Regardless you are probably up for $250 or so for a replacement screen. ($450 if you get it replaced with a genuine Pixel 3 screen at the one official repair centre in Oz (I know cause I just did exactly that)