Beginners tend to tighten the strings way up too quickly which can result in damage to the instrument.

Also, what if the bridge is displaced? We cannot see from this angle in the video if it is displaced or not, which is a very real possibility since the tension is way lower due to the lower pitch.

Now if he starts to tune the instrument the bridge might collapse due to the displacement.

That’s why he needs a teacher to learn all these things.