On this video, we can clearly see the payload being disposed, but I fail to understand how it gained so much momentum as the Canadarm appears to not be moving. The video mention a new procedure, can anyone find it ?
This answer addresses the "how it gained so much momentum as the Canadarm appears to not be moving" part of the question.
The array was separated from its Flight Releasable Attachment Mechanism (FRAM) using a Lightband deployment mechanism, a spring-loaded device that imparts a velocity to the array.
-From second reference:
Since stowage inside the trunk of Dragon was impossible in the deployed state, NASA made the decision to jettison ROSA into the atmosphere from its FRAM using a built-in custom Lightband mechanism.
-From first reference:
All-inclusive product The ALB has integrated Separation Springs, Switches and Connectors and does not require additional brackets or complex interface documentation. This reduces complexity, increasing reliability and decreasing mission cost.
(emphasis mine - ALB = Advanced Lightband)
I do not have a reference for what the "new procedure" was, but every payload has new procedures written for it - possibly this refers to the payload-specific jettison procedure.