I mean, wow. There's so much going on here. But the take-home is that people who create hate propaganda can manipulate anyone to try horrible things.
If this guy succeeded, it would have been an antisemitic attack, and his having had a 93 year old Holocaust surviving grandfather would not change that.
New York Post : Man who allegedly threatened NYC synagogue is Jewish, kin of a Holocaust survivor: Lawyer.
https://nypost.com/2022/11/20/matthew-mahrer-who-made-threats-against-nyc-synagogue-is-jewish-kin-of-a-holocaust-survivor-lawyer/