I saw a hologram of my grandpa when he was actually 30 feet away

When I was 7-8, I had a very strange experience. During the summers, I'd spend a lot of time at my grandparents' house. My grandpa used my mom's old room as his computer room. He had a desk just inside the bedroom door. He always left the door open and would spend several hours in there playing solitaire and looking at classic cars online. They had a next-door neighbor who was a lifelong friend that would come over every afternoon, and the three of them would sit outside on the front porch and talk. Right before the neighbor arrived, my grandma had been on his computer for several hours. We were all out on the porch and my grandma asked me to go inside and pour him a glass of iced tea. I did, and when I passed his computer room on the way back outside, I glanced over and he was sitting in his computer chair. I could see the light from the computer screen on his face and glasses even though it was turned off. There was a static look to him, and I could see glitches on him. Best way I can explain it. I froze and stared for 3-4 seconds. He never made eye contact and disappeared. I took the tea outside to him and he was in his porch chair and had been the whole time. What happened?