The idea of looking through a small hole to see spirits is very old.
Some claim it is looking through time itself, backwards of course. If the wood of that fence is very old, it could be connected to the times it experienced.
Some claim it is forcing our minds to focus on one specific area, how often do we look at the spirit world, one image at a time? We take everything in around us, every detail, and cracks or holes don't allow us to. The spirit world on the physical plane or how most call it "astral" is full of physical people's energy and spirits. Unless a spirit interacts with you, if it seems to ignore your presence, it is most likely just an impression.
The spirit world itself, most call this the ethereal plane, lacks the "garbage" of discarded energy from physical emotion, thought, and action. And its far easier to know what you're looking at lol
It could have been an impression. Impressions are energy imprints. We are made of energy, everything we touch, we leave behind a little of that energy, and everything we do emits energy. Sometimes we can pick up on this energy again, even centuries later. This is how most intuitives get their information from when reading past events or the history of objects, people, or buildings. There is a multitude of energy all around us. When I astrally projected for the first time, my home looked entirely different. It looked like I stepped into the 1960s. The walls were painted lime green and the furnature was disgusting! Lol. This is just an example of how the energy of our world continues to linger. The stronger the thought and emotion behind the energy the stronger the energy. A woman getting ready for her wedding is a very special time, and would have quite a lot of thought and emotion from all people involved.