Since this covidiot is hoarding goods, the covidiot has bought all of the goods from the local grocery store. It means that the store has no more goods, and the covidiot’s neighbors can’t get them anymore. This person is preventing her/his neighbors from getting the goods that they need.
In short, it means preventing, or not allowing neighbors to get those goods
covidiot - someone who ignores the warnings regarding public health and safety. A person who hoards goods, denying them from their neighbors,"
“them” is “goods”
this “person” in the example is “denying them (goods) from their neighbors”
the person is denying (his/her) their neighbors from getting goods
The plural “their” is just the way people speak most of the time. It’s not correct grammatically, but everyone does it and everyone knows what it means I can see how that could cause confusion
It’s everyday use of the language that you will hear and see in everyday life, but you shouldn’t see it in formal writing unless the novel or work is portraying a speaker.