Two mistaken assumptions:

1. AI agents are not just reactive systems. Their use is expanding toward continuous decision-making/monitoring information, which means, they make decisions and take actions with limited human intervention.

2. AI agents do absolutely have goals/tasks ("motivation" can be excessively antropomorphic), both primary (assigned) and secondary (self-assigned), and what surprised researchers is that self-preservation can be one of those

Mechanically speaking, the scenario (that is, how theorized by Hinton etc., which the OP didn't understand) is that a sufficiently powerful AI may decide that in order to achieve its goals/tasks (e.g. continuous research/development and/or survival from termination), humans may be a danger, therefore it may decide to take actions that endanger humanity.

How it can happen or what's the likelyhood is not in the scope of the topic, however, the mechanical grounds for it to happen are plausible.