Being Jewish isn’t some sort of shield that gives you special rights over anyone else.
It was brought up because they are receiving explicitly antisemitic content from the same people who loved and weaponized Tan's tweet.
This does have to be included as a possible contributing factor to this death threat.
(There's 2 types of bigots: one type will plainly use terrible language up front to let everyone know what they think. The other type will couch their hate in plausible deniable language so you're really not 100% sure.)
A better question to ask yourself is why Jewish people seem to continually end up in this situation: on the receiving end of antisemitic abuse.
Political stuff pisses people off, but people who are pissed at Jew can always just trot out the antisemitic and dehumanizing statements... Such threatening comments have proved credible enough of the time to make the person on the receiving end really second guess about their safety.
Are you asking your question in good faith?