This is a fallacy stating “since event Y followed event X, event X caused event Y”.
It is a particularly dastardly fallacy because human minds often learn by assuming cause when an action precedes an event. If I press a button, and a light turns on, I may believe that pressing the button turned the light on.
This is an issue when our pattern matching brain decides that we won the football game because we wore this particular pair of socks, or the sun rose because the rooster crowed.