Mr Canning said the pursuing officer genuinely thought the man was drowning, having lost sight of him in the heavy rain. Weighed down by police gear, including a heavy stab-resistant vest, the officer could not reach him and had to retreat.
The police, Cobden volunteer firemen and the Coastguard then spent the night in heavy rain searching the lagoon in vain. The search resumed on Saturday.
Mr Canning said they now believed the man's family had driven him back to Christchurch on Saturday afternoon, or Sunday.
He was in Greymouth with family, and also had relatives living here. The crashed car belonged to a relative.
The Greymouth Star understands he had been at a party in Cobden earlier in the evening.
Mr Canning said he had a "pretty good idea" why the man ran from the police, but could not say more in case he prejudiced a future court case.
Asked if it was true the police had retrieved the man's trousers from the lagoon, he said "we have got some items we believe are his".
Until they had spoken to the culprit, it was unclear if he had really been in trouble or was pretending to be while effecting his escape.
Mr Canning said the costs of a search were not normally recovered, but if the man appeared before court on a charge of wasting police time, the court may consider restoration.
Coastguard skipper Doug Griffin said his men spent a combined 121 hours looking for him, stopping only when light faded on Saturday night, before resuming at dawn yesterday.
It was so dark when they were first called out after midnight on Friday that they had to borrow a light and generator from the fire brigade. They gave up at 4.30am, and were back out at 7.30am. They only finished searching about 2pm yesterday.
Mr Griffin said he would have expected the man's family to have had the courtesy to call - "even if it was anonymous".
Cobden Volunteer Fire Brigade fire chief Gary Pollock said their nine volunteers gave up 31.5 hours in the cold and rain, having joined the search at 12.45am on Saturday.
"We were checking around the edges."
The Solid Energy Rescue Helicopter was also sent up for about 40 minutes on Saturday afternoon. From the air, the pilot could see right to the bottom of the lagoon. The land search and rescue team was also involved.
The 'missing' man's age was not available this morning, but police said he was under 25.