So the arrested man is named as "Keith Beviss" (aged 55 or 54 depending upon which article I read) from Honiton who from the artist's court sketch looks like a non-descript overweight balding white man that I would pass in the street without a second glance.
A couple of the articles mention that one line of enquiry is a religious hate crime and another article mentions that one nearby interviewed shop worker said that they had noted several with mental health problems in Honiton since moving to the area.
My take on this is that Honiton is a "sleepy" market town that is unlikely to have any terrorist knifings such as from extreme Muslims. (If there were I believe it would be in the main shopping area where more people could be found to attack.)
I suppose it could be a burglary and that the alarm was set off and the installer went to investigate but the distance from Westward Ho! (where Philip Ryan's business was based) to Honiton is at least 50 miles so I cannot see it being an alarm going off and the perpetrator being disturbed.
So I lean towards mental health issues. The fact that the arrested man seemed to still be in the area and there was no apparent police hunt makes me wonder whether there was an altercation ending in a stabbing and whether the man himself called the authorities or waited around (a camper van was mentioned) and gave himself up.
But I do wonder if this is a random chance occurrence (wrong place, wrong time) or whether it might have been exacerbated by unhappy dealings between Keith Beviss and Jehovah's Witnesses. But as Philip Ryan was an elder in a different part of the county I doubt if the two were known to each other.
Who knows at this stage?