There's plenty of ways to enter in many buildings without "working there". As long as the physical security there is lower (and there's a ton of reason why it could be) or that it's already open to the public.
> I think sending a parcel like in this article,
That only give you physical proximity. Unless they have bad wifi securities like that article said... that won't give much. People don't talk about password regularly ;).
> leaving a USB stick lying around is often an easier task
That's just hoping right there, Windows autorun hasn't been a thing for a long time, an USB keys that open a terminal is freaking obvious and most people know not to plug any random USB keys. That most probably won't works for any high ranking official.
Almost no one talk about making sure windows doesn't see keyboards though... or even screens, and you'll see that usually, people with higher ranks do have windows closeby ;) (the perks of the ranks).