So, let's analyze this sentence:
If translated into Chinese, this sentence should be "How did your hair grow so fast?"
The grammar of the analysis of the Ark in the World is correct in itself, and el pelo is the subject. Removing the indirect object te can simplify the sentence to "como puede crecer tanto el pelo", which means "Why does hair grow so fast?"
If you want to modify the subject, take this sentence as an example to express whose hair this is. Spaniards are not used to using the sentence "como puede crecer tanto tu pelo", although there is nothing wrong with this sentence grammatically.
In Spanish, the idiom is: take body parts as the subject, such as hands, feet, hair, stomach and so on. The displacement verb is the corresponding intransitive verb, with the owner of the body part as the indirect object (also called indirect complement).
Let me give you another example to deepen your understanding:
I like Cabeca.
Explanation: You may have said this sentence a long time ago, but you may not realize that this sentence is grammatically the same as "Como te puede crecer tanto el pelo". This sentence can also be simplified as "duele la cabeza" (headache). Who has a headache, add an indirect complement me, which literally translates into Chinese meaning "headache also affects me" and the implication is "I have a headache".
Note: vetroni may have no problem understanding this grammar himself, but the example he gave is not an example of this grammatical phenomenon.