> "Unique_ptr is such a fundamental type that, if one claims to be a c++ programmer, one has to know it and understand how it works."

No.

Those utilities weren't standardized before C++11. People wrote their own implementations before that. People had to understand stack unwinding and scoping, memory, RAII, design patterns that relate to allocation/de-allocation of memory, ownership transfer.

Then came in the people that decided it'd be a great idea to start quizzing others about C++11 concretions.