If they're referring to the incident at SOGO before the start of the march, there were scuffles and pepper-spraying that preceded the use of tear gas. It was the usual situation of police getting yelled at by a crowd after splitting into small groups and arresting people.
This is my recollection, too. There was also a person down on the ground and being isolated by the cops (I could not figure out the situation). The most significant difference is that the street was not packed tight with people like on 12.01