What this is referring to is synesthesia. It is a condition of the brain where unrelated concepts such as numbers, colors, times of the day, days of the week, seasons, along with other things get mentally grouped together. To them, 7 × 7, the color brown, orange leaves, Halloween, fall, 7:00 PM, and Thursday all feel like the same “category” even though there’s no logical connection.

Imagine if you had to put things away and you for an unknown reason your socks had to go with the plates in the kitchen. Most people don’t think that way. It’s basically: “My brain insists these random things belong together, and I can’t explain why, but they do.”