I don't know how much he learns from the telly
but he's very likely aware of the Wick Effect. In a BBC interview he said he referred to Professor Bernard Knights book on forensic pathology. The Wick Effect is described in the section on "Atypical Localized Burning an Spontaeous Combustion". The book is obviously dismissive of the spontaneous element but recognizes that many cases in this category are on record.
It's not uncommon in the medical field for descriptive terms to loose their original meaning but still remain in use. For example 'coma' means deep sleep but a person in a coma is not in a deep sleep and the brain shows disorganised patterns of activity totally unlike those of sleep. But nobody would deny a person is in coma by focussing purely on the literal meaning of the term.
Similiarly the term "spontaneous human combustion" appears to have become a catch-all category for all the strange instances of fatal burning that have occurred in apparently inexplicable cases where the ignition source is destroyed. One can easily think of better terms but unfortunately it this one that has stuck.
The most complete test of the wick effect that I have come across was published in the Journal of Forensic Science with a summary on pubMed. A pig carcass was used in the experiment.
The similarity of pig fat and muscle tissue to those in humans is well recognised. (In fact on a morbid note, scientists involved in terminal ballistics research with the goal of killing or maiming humans, have used pigs as a substitute for humans in their tests.)
But in the Wick experiment a necessary condition was 1L of fuel to provide the sustained temperature and burning to initiate the wick effect. If this article represents the best understanding of the effect in peer-reviewed literature, then one can see why having no evidence of an accelerant presents a problem in this particular case.
There has to be some mundane - possibly the wick effect or possibly still unknown - cause to this and similiar cases. There has to be because as someone pointed out, nowadays if this were divine intervention we'd be seeing it every day
Edit: p.s. the article is still available on the indo site. Link may have changed:
http://www.independent.ie/national-...rom-spontaneous-human-combustion-2886192.html