Difficult to tell what happened without knowing the full context.
It has happened that scammers call support, say they’re XYZ and lost their 2fa device. 2fa gets disabled and they can overtake the account in some old fashioned way.
Also there is SIM splitting and other techniques. Also the youtuber could be wrong. These attacks are very subtle until it’s too late.
Give us a link (with timestamp if it’s long), maybe someone can find out more. [Edit: Thx for the link.]