Yeah exactly – for screenreader users, and for sighted keyboard users (eg. for people who have a hand tremor and can’t keep a mouse steady)
If you don’t typically use the keyboard for stuff, then it makes sense that you wouldn’t have an immediate sense of what keystrokes are obvious for certain things.
But frequent keyboard users are more likely to. For example, checkboxes are activated with Space, Enter is used to press buttons (and sometimes Space is used for that as well), so these are the logical choices.
Having said that, there is a case for saying that this kind of interaction could have instructions. Perhaps a popup tooltip that appears the first time you Tab to an item, that explains what the keystrokes are.