Okay. 'A short rest is a period of downtime, at least 1 hour long'. 'A long rest is a period of extended downtime, at least 8 hours long'.
The 'downtime' part is made of the same 'stuff', the only difference is that an hour of that 'stuff' gives you the benefits of a short rest and 8 hours of that very same 'stuff' gives you the benefit of a long rest.
It isn't that the 'stuff' is different; the 'stuff' is the same.
The 'stuff', in each case, is 'avoiding strenuous activity'. It isn't really 'doing something' that gives you the benefits, it is '
not doing anything stressful' that gives you the benefits.
What is 'stressful activity' is the
same in regards for both long and short rests.
The difference is that
any strenuous activity spoils a short rest, but it takes more than an hour's worth of strenuous activity to spoil a long rest. But the 'strenuous activity' is the same 'stuff' for both types of rest.
If I visit my local casino I get my reward card stamped on each visit. If I get three stamps I get a free drink. If I get 7 more stamps (10 total) I get a free meal for two.
These stamps are the same kind of stamp! There aren't two different stamps. The receptionist doesn't ask me if this stamp is for the meal or for the drink. I keep my stampcard after my third stamp and keep collecting for the next reward.
'Resting', in both natural language AND 5E RAW, is 'avoiding strenuous activity'. If you collect 1 hour of it then you get the benefits of a short rest. If you collect 8 hours of it then you get the benefits of a long rest, even if you
also got the benefits of a short rest within that time.
Short Rest said:
A short rest is a period of downtime, at least 1 hour long, during which a character does nothing more strenuous than eating, drinking, reading, and tending to wounds.
Long Rest said:
A long rest is a period of extended downtime, at least 8 hours long, during which a character sleeps or performs light activity: reading, talking, eating, or standing watch for no more than 2 hours.
In each case, you can do stuff, as long as that activity is not considered 'strenuous'. Each gives examples of activity which is
not strenuous enough to spoil the rest, but these are examples, not a prescribed list of mandatory activity!
So, RAW, there are
not two different types of inactivity! The only difference is that you get different benefits for accumulating greater amounts of the same kind of inactivity.