Because you are remembering the last time you filled out that paperwork and how it reminded you of that particular event.
Memories are always being rewritten and reshaped. Most of the time when you think of a memory, you aren't really remembering the original memory, but instead remembering the last time you remembered it. It is the only way to keep a memory fresh. And you will often end up adding details to the memory as you forget the original details, perhaps even eventually changing the memory to one that is considerably different from what actually happened. Hence false memories.
The two events are somehow related, no matter how far apart. Like it's a line, you think of start line and of that marathon. Or you may think about honey, go to bees, then The Bee Movie, then another unrelated movie. It all happens in your brain during that milisecond you thought about honey so you don't realize it