As u/pseudo0, there is a required element of imminence, and the precedents are fairly clear. The tweet in question would not have resulted in prosecution in the U.S. For example it's quite common for U.S. presidents to get death threats like this even, and the secret service will go and interview those who do that, but then if it turns out they didn't have a plan, means, or real intent, then they do not prosecute them. In the U.S. you can chant "death to [fill in the blank]" all day every day if you like, and it's not a crime until you're chanting that at the head of a mob, and then it's a very serious crime with stiff jail time.