We calculate the double differential distributions and distributions in recoil moments for the high energy non-relativistic double photoionization of helium. We show that the results of recent experiments are the pioneering experimental manifestation of the quasi-free mechanism (QFM) for the double photoionization, predicted long ago in our papers. This mechanism provides a surplus in distribution over the recoil moments at small values of the latter, corresponding to nearly back-to-back emission of the electrons. Also in agreement with previous analysis the surplus is due to the quadrupole terms of the photon-electron interaction. The confirmation of the QFM existence opens a new area of experimental investigations of this mechanism. QFM leads to a maximum at the middle of the outgoing electrons energy distribution. As is shown, the relative role of the QFM becomes more important with the photon energy growth. Thus, it is expected to be bigger for ω above the investigated now the 1 KeV region. As is demonstrated, with further ω growth a minimum with appear in the middle of the central peak of the energy distribution, caused by the non-dipole nature of the QFM. We hope also that contribution of the QFM to the total cross section, resulting in a slope of the double-to-single photoionization ratio will be measured. We expect the detailed investigation of the relativistic ω region, where the QFM contribution will become as important and then even stronger than the usually considered shake-off mechanism of double-electron photoionization. Investigation of the QFM enables to clarify the behavior of the wave function of the helium atom near the singular electron-electron coalescence point. This is important for precise computations of the atomic characteristics.