Police said on Sunday they did not consider the attack to be a terrorist incident.
Overnight, police said nine of the 10 people injured on Saturday were in a life-threatening condition.
British Transport Police Superintendent John Loveless said four of those have now been discharged and one other person had arrived at the hospital on their own, taking the number injured in the attack to 11.
He also said the two people arrested remained in custody and confirmed they were born in the United Kingdom.
One is a 32-year-old Black British man, the other is a 35-year-old man of Caribbean descent, he said.
"There is nothing to suggest this is a terrorist incident," Loveless said.
On Saturday night, bloodied passengers had spilled out of the long-distance train when it made an emergency stop in the town of Huntingdon, 120km north of London, where dozens of police waited, soon after multiple stabbings were reported on board.
The police force said "Plato" - the national code word used by police and emergency services when responding to what could be a "marauding terror attack" - was initiated.
That declaration was later rescinded but no motive for the attack was disclosed.
The attack took place as the train from Doncaster in northern England to London's King's Cross station was about halfway through its two-hour journey and approaching Huntingdon, a market town northwest of the university city of Cambridge.
Passenger Olly Foster told the BBC he heard people shouting "run, run, there's a guy literally stabbing everyone".
He said he initially thought it might have been a Halloween prank.
But as passengers pushed past him to get away, he noticed his hand was covered in blood from a chair he had leaned on.
Emergency services, including armed police and air ambulances, responded quickly as the train drew into Huntingdon.
The attack appears to have been contained swiftly after the train arrived at the station, and police officers wearing forensic suits, with a police dog, could be seen on the platform.
British Prime Minister Keir Starmer said his "thoughts are with all those affected" after the "appalling incident".
Paul Bristow, the mayor of Cambridgeshire and Peterborough, said he had heard of "horrendous scenes" on the train.
London North Eastern Railway, or LNER, which operates the East Coast Mainline services in the UK, said there would be major disruption on the route until Monday.
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