Does Zen have an unusual view of samadhi? There was a book titled Zen in the Art of Archery:

Zen in the Art of Archery is a short book by German philosophy professor Eugen Herrigel, published in 1948, about his experiences studying Kyūdō, a form of Japanese archery, when he lived in Japan in the 1920s. It is credited with introducing Zen to Western audiences in the late 1940s and 1950s.

Not only archery, there are other lay activities too which I somehow think of as associated with Zen, for example: tea; gardening; poetry; sitting; sword-play; calligraphy and painting; maybe music; ...
I just read this comment:

Samadhi means “absorption,” but fundamentally it is unity with the whole universe. When you devote yourself to what you are doing, moment by moment — to your kōan when on your cushion in zazen, to your work, study, conversation, or whatever in daily life — that is samadhi. Do not suppose that samadhi is exclusively Zen Buddhist. Everything and everybody are in samadhi, even bugs, even people in mental hospitals.


Is this statement even true (or is it mistaken), according to Zen?

If it's true, do other schools of Buddhism have a similar or comparable view of samadhi?
I get the impression (perhaps I'm wrong) that some traditions see samadhi as associated with meditation, and meditation as distinct from (even deliberately renouncing) any other activities.

When I answered this question I wanted to say something from my 'personal' experience of becoming absorbed in or engaged with some activity. I decided not to because this is a site about Buddhism and so an answer based on only my personal activity or experience might be off-topic.
I know next to nothing about Mahayana (e.g. Zen or Tibetan) Buddhism. Can you reference some recommended text on the subject of &quot;absorption&quot;, absorption in lay activity? Maybe something that might help to answer Rishi's question?

The only theory I have heard of about activities (apart from that it's virtuous to engage in activities which are helpful or beneficial) is Flow (psychology). But that is not (so far as I known) a Buddhist theory. Does Buddhism have anything to add to or to contradict that theory, analogous?

If absorption in activity is (kind of) legitimate, what's the important difference between sitting (meditating) on a cushion and e.g. sitting at a potter's wheel, or sweeping the floor, or whatever?
'Samadhi' generically means 'collectedness' or 'concentration'. 

The Pali states there are two types of concentration, namely, 'right' &amp; 'wrong': 


  In one of right concentration, wrong concentration is abolished...
  
  MN 117


'Right concentration' is defined as concentration that has seven supporting &amp; requisite factors:


  Any singleness of mind equipped with these seven factors — right view, right resolve, right speech, right action, right livelihood,
  right effort &amp; right mindfulness — is called noble right concentration
  with its supports &amp; requisite conditions.
  
  MN 117


Therefore, an expert marksmen trained to assassinate people in war has 'samadhi' but it is 'wrong samadhi' because it is not supported by the above seven factors. 

In fact, if a 'Zen samadhi' is not supported by the above seven factors, particularly 'right view', it is not 'right concentration' according to the Pali. 

As for the word 'jhana' or 'absorption', this generally refers to a 'meditative' concentration.