Memory is indeed a strange & fascinating thing.

As the replies above state it's emotional connection which makes some memories stronger than others. This is why someone with dementia often remembers events from their childhood/young years (when we are very impressionable) but may not remember what happened yesterday - not that you have dementia, but I use this as an illustration of how some memories remain when others don't.

As to what triggered these memories when you say the person was unconnected to your father I can't say. Could it be that you are feeling generally more sensitive & emotionally charged?