Either the person is living in a fantasy world, or perhaps they are noticing the subtle changes that come about from changing lighting/mood/color of clothing or even the changes brought about by altering the chemicals within the body. It is also possible to do illusory spells, but they take a lot more effort than most kids are willing to put in these days.
It is not completely impossible for your eye color to change. While it is not likely to go from brown to blue, or vice versi, our eyes do change hue when chemicals are added or subtracted from our body. Physical and emotional pain can appear to cause a whitening around our irises, known as a sodium ring. Also when your pupil restricts or dilates it causes it to look a bit different due to the compression and decompression of the iris.
It is called biokenisis, I bro Calvin-nii creats sibliminals on youtube, his channel is Subliminals Central.
Biokenisis is a very long process of body manlipuation. It can be shortened with Calvin-nii's uploads, and his explanations ov what, subliminals, binurals, brainwave entertainment, chi and other things are.
Anyone can say anything on YouTube, and YouTube videos are easily falsified. The fact of the matter is that you cannot alter your eye color through the use of magic. There is in fact no scientific evidence that biokinesis exists.
Just to toss my 2 cents in there, I believe if you have hazel eyes you can influence a change. Though not a permanent one. I have been in relationships with women who's hazel eyes would switch from brown to green depending on their mood....or (pls dont hit me ladies) their monthly cycle.
So based on this I would say that there is cause to believe that it can be influenced.
Eye colours can naturally change as a response to the environment as well as age:
Children are born with blue eyes that shift to become their perminant colour not long after they are born.
Elderly people with blue eyes tend to find that it goes lighter as they get older.
Chemicals like chlorine water in swimming pools can make your eyes appear to change colour for a short period of time.
But no kinesis exists and no spell can change your eye colour, it is a genetic trait that cannot be altered. On youtube anyone can say anything whether it is true or not, so personally I wouldn't trust anything about witchcraft on there with a barge pole.