Here is the answer from Radpowerbike EU, thanks.
"You have probably informed that Throttle can go full speed, and that is true but here in EU we call that Twist Power Assist.
Twist Power Assist on the European versions of the bikes is limited to 6 km/h. This means the Twist Power Assist on your bike will serve a walk assist function, or to give you a boost when you are starting off. This limitation is done so that the bike can be categorized as a standard e-bike throughout Europe, and does not require any registration or insurance."
"You have probably informed that Throttle can go full speed, and that is true but here in EU we call that Twist Power Assist.
Twist Power Assist on the European versions of the bikes is limited to 6 km/h. This means the Twist Power Assist on your bike will serve a walk assist function, or to give you a boost when you are starting off. This limitation is done so that the bike can be categorized as a standard e-bike throughout Europe, and does not require any registration or insurance."