The clothing was seized by police and Coroner Scott ruled the jacket was in fact not high-visibility at all.
Coroner Scott said Mr De Thierry was killed "because Mark was running on the formed roadway within the fog lines" and "he did not move off the roadway ... when Mac saw him".
Mr De Thierry took "evasive action", having only seen Mr Richardson at the "last minute because of the dark clothing and the dark conditions".
Mr De Thierry swerved right and then left, which was described by police as "a reflex action to seeing the person on the side of the roadway".
"Mark, of course, did not intend the consequences," the coroner said.
"Mark should not have been running on an unlit rural road in the dark."
The finding also said that "at the very least", Mr Richardson should have been wearing high-visibility clothing with reflective stripes and he should have stopped running and left the road completely when traffic approached.
After the crash, Mr Richardson told Reon Hodge, the first motorist to arrive at the scene: "I think I might have caused that."
Mr Hodge said Mr Richardson identified himself and then kept repeating statements like "he had to go".
Mr Hodge "became annoyed and ... told Mark to leave, although the language he used was much stronger than that", the coroner said.
All Mr Hodge could do after phoning emergency services was to comfort Mr De Thierry until he died a few minutes later.
Mr Richardson left the scene but later that day reported his involvement to police.
Coroner Scott said Mr Richardson "should have behaved very differently at the scene".
"What he should have done is quite obvious," the coroner said.
"However, what happened was totally unexpected, it was catastrophic and no doubt it was hugely emotionally distressing to Mark.
"His reaction did not affect the outcome as [Mr Hodge] remained and sadly Mac was beyond help."
Mr Richardson accepted responsibility during reconciliation with Mr De Thierry's family before the coroner's inquest.
Coroner Scott said Mr De Thierry's death should serve as "a wake-up call for all runners on rural roads".
"I do not believe running on rural roads is a safe practice, certainly not at night but even in daylight," he said.
Coroner Scott concluded his finding by thanking Mr Richardson "for the candid way he gave his evidence and for the candid way he accepted responsibility for what happened".
It was reported earlier this year that Mr Richardson would not be charged with Mr De Thierry's death.