How did the professor stumble upon the Egypt game?

The professor stumbled upon the Egypt Game while looking for something in a storeroom in the back of his antique shop. 
Since he was not used to being in the storeroom, his curiosity was piqued when he heard a noise coming from outside the storeroom. The text tells us that the storeroom overlooked an abandoned yard surrounded by a fence and that there was a dilapidated lean-to shed in the yard. 
Since the storeroom window was caked with grime, the professor had to rub out a spot in the thick coating of dirt before he could look through the glass. As he looked through the window, the professor saw two girls (of about eleven or twelve-years-old) and a little boy (of about four-years-old) coming through a hole in the fence.
The professor had seen both of the girls before; the first, called April, once entered his store, while the other, an African-American girl, was a resident in the neighborhood. The little boy, also African-American, was undoubtedly the second girl's brother. Because he had a customer waiting, the professor had to make his way back to the front of the store.
Later, after the customer left, the professor made his way back to the storeroom. From the storeroom window, he could see that the children had made changes to the surrounding yard. They had propped up the lean-to shed with some old porch pillars from the yard and placed a statue of Diana next to it. In the back and center of the shed, the children had placed a chipped, plaster bust of Nefertiti ensconced in a broken birdbath. They had also weeded the yard and placed a thistle flower offering before the Nefertiti birdbath. 
So, the professor stumbled upon the beginnings of the Egypt Game while looking for something in a storeroom in the back of his antique shop.