But he states that this is not acceptable, because we don't know what is touch at macroscopic level, hence it makes no sense to explain it via microscopic level. He states that QM is valid only at atomic scales, [...]
So basically he doesn't agree to explain touch with QM and microscopic theories, also questioning that "if we don't touch, how do you explain intermolecular bounds?"
The opposite is true. In the video interview series Fun To Imagine, Feynman famously and eloquently stated the state of affairs that is actually happening in physics. The sensation of touch, that your hand does not pass through a chair, is a consequence of the microscopic kind of electromagnetic forces. There is no understanding of electromagnetic forces in terms of touch; we can only possibly hope to understand touch in terms of microscopic electromagnetism.
In fact, even that is an approximation. Feynman decided to stop there, but if you actually go into the details, you will realise that the quantum mechanical, Pauli Exclusion Principle, repulsion is about as strong as the microscopic electrical repulsion when it comes to actual touching. The repulsion energy that is rising, is only understandable and explanable from microscopic quantum theory.
There is a standard quip that we tell beginning university physics students. That when something is any one of big, heavy, and/or fast-moving, we will have to consider relativity. Similarly, if something is small, we have to consider quantum theory. However, we always leave vague the delineation. Fast-moving is the easiest, because we can simply compare speeds with the speed of light in vacuum, and immediately we will have some idea of whether something is fast enough to require relativistic corrections, or to use fully relativistic considerations.
But when it comes to whether something is small, the criteria is actually that "The number of particles in a given volume is big enough". In particular, if you have a gigantic number of particles, then even if the volume is large enough to be macroscopic, it is still small enough that we have to use quantum theory.
For example, every piece of metal that you touch, every insulator, every semiconductor that makes up your computer or phone, every solid, every liquid, the whole concept of touching anything at all, can only be fully explained if you consider quantum theory. There is no way to explain the "sea of electrons" in a metal without quantum theory. There is no way to explain even the simplest covalent bonds without quantum theory. It is a degree of freedom that is hithertho unavailable in classical reasoning, that is opened up in quantum theory, that allows covalent bonds to even be a thing at all.
So your friend is just way too wrong to even begin to understand how wrong he is.
In fact, the vagueness of the definition is necessary: For example, a neutron star is big and heavy, definitely requiring the General Theory of Relativity in its description, but at the same time so dense that it can only be explained with quantum theory. Only via quantum theory can its immense gravitational pressure be balanced, not by electrons and protons holding it up, but that during its formation period, the electrons get compacted so small that it goes relativistic, and in a sudden flash, the electrons gets squished into the protons, turning them all into neutrons and stablising in the form of neutrons, as opposed to hot hydrogen gas. Stars that turn into neutron stars, are heavier than about 1.44 times the mass of our Sun. That number is called the Chandrasekhar limit. Is your friend trying to say that the Sun is not macroscopic enough for him?
