Watch two sets of responsibilities
Law 14 requires the tackler to release and move away or get up, while the tackled player must make the ball available immediately. Watching only one player can hide the conduct responsible for the penalty.
Imagine a carrier on the ground with the tackler still wrapped around them. In a second sequence the tackler releases and moves clear, while the carrier keeps the ball pinned beneath their body. Both pictures may end with a whistle beside the same pair of shirts.
The first clear view may come too late
A replay beginning when arriving players reach the contest can omit the initial release or failure to release. Trace back to the moment both tackled players went to ground. The order of those actions helps explain why the referee points one way.
This is a viewing explanation, not contact technique or health advice. It does not turn a short camera clip into a complete adjudication of every possible infringement. The useful habit is to track the tackler and carrier separately before looking at the later contest. A single phrase such as holding on may otherwise be mistaken for a description of the wrong person.
Questions answered
Does only the ball carrier have an immediate duty?
No; the tackler has separate release obligations.
Why rewind before the arriving players?
The relevant release action may already have happened.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.