C++ std::scoped_lock allows nesting

Question

#include <iostream>
#include <mutex>

using namespace std;

class TestClass {
    public : // members
        std::mutex m_mutex;
        int m_var;
    public : //functions
        TestClass()
          :m_var(0) {};

        void fooIncVar()
        {
            cout << "calling inc var" << endl;
            std::scoped_lock lock(m_mutex);
            _incVar();
        }
        
    private:
        void _incVar() 
        {
            std::scoped_lock lock(m_mutex);
            m_var++;
            cout << "var : " << m_var << endl; 
        }
    
};

int main()
{
    cout<<"Hello World" << endl;
    auto a = A();
    a.fooIncVar();
    return 0;
}

I am trying to understand how scoped_lock works with a mutex. I was expecting that below program will just hang because I am calling _incVar by holding the mutex in fooIncVar since scope of the variable is until the end of the function. But that doesn't seem to be the case. I get the following output

Hello World                                                                                                                                                                                                             
calling inc var                                                                                                                                                                                                         
var : 1