The important part is local time plus timezone.
The offset is there only for the very rare case that you save a time that you know is ambiguous when you save it. And when DST rules don't change. Usually it happens when you change from DST to non-DST in the autumn and a certain hour happens twice.
In the example, the offset will not be used. Only local time plus time zone.
edit: I have updated the article to explain this part.
Saving local time plus offset is _exactly_ the same information as saving GMT, isn't it?
You'd really need to save local datetime plus location... which they don't seem to actually be recommending?
Of course, for actually triggering an alarm or whatever, you'd still need to plot this on the actual timeline somehow, and deal with periodically checking to see if it should be changed because of a DST or timezone rule change or whatever.