I don't understand. Why is it the tradition of 'otting' and not 'spotting'? It seems like the appropriate rule for forming the suffix should be to take the maximally sized word fragment common to all instances.
In considering, say, the set of words undergo, understand, understudy, underground, we would not identify the relevant prefix as 'und' - shortening of the true prefix 'under' not only lacks a rational basis, but it loses the sense of the prefix.
The same is true if one shortens 'spotting' to 'otting'. Whoever wrote the article in question sacrificed intelligibility for what? Some effort at smirking cleverness?
Improbable Research: 'In the June 28, 2008 issue of BMJ (the publication formerly known as the British Medical Journal) Barrie Smith, a retired physician from Birmingham, describes—though he does not name—a new form of the grand British tradition of otting. The proper name for it is obvious to anyone who reads Dr. Smith’s description: windowspotting.
'The best known of otting traditions is trainspotting. Some British citizens also practice planespotting, busspotting (a practice that now draws disapproval from the British Government, which views bus spotters as being possible terrorist spies) and other varieties of otting. These may all be descended from the ancient practice of bird spotting, also known as bird watching.'