I don’t doubt something happened but the whole thing sounds kind of far-fetched. Seems some details were left out like why was this homeowner targeted in the first place?
The only thing you have to do to attract attention from MS-13 is stare at one for a microsecond to long. In this case I think the cousin is the key.
Maybe he cut them off in traffic. I was making a perfectly legal right turn onto an Albuquerque boulevard one day and it conflicted with an illegal u-turn being made by the driver of a car full of gang bangers. I didn't yield to them which cut him off and forced him to hit the brakes and fall in behind my truck.
That really made them mad and they followed me several blocks taunting me to pull over. They even drove up into a parking lot parallel to the street to try and get ahead of me on the right side of me.
If you look too long at any of these thugs, you become a target. They will use any excuse to cause harm to another.