The part of the data collection and its consequences to the result of the experiment, as presented in the video you provided, seems to be wrong. At least it never happened the way, the speaker wants to make us believe.
Chapter from the Wikipedia Article about the Double-slit experiment:
"Which-way" experiments and the principle of complementarity
A well-known thought experiment predicts that if particle detectors are
positioned at the slits, showing through which slit a photon goes, the
interference pattern will disappear.[ 2] This which-way experiment
illustrates the complementarity principle that photons can behave as
either particles or waves, but cannot be observed as both at the same
time. Despite the importance of this gedanken in the
history of quantum mechanics (for example, see the discussion on
Einstein's version of this experiment), technically feasible
realizations of this experiment were not proposed until the 1970s.
(Naive implementations of the textbook gedanken are not possible
because photons cannot be detected without absorbing the photon.)
Currently, multiple experiments have been performed illustrating
various aspects of complementarity.
An experiment performed in 1987  produced results that
demonstrated that information could be obtained regarding which path a
particle had taken without destroying the interference altogether.
This showed the effect of measurements that disturbed the particles in
transit to a lesser degree and thereby influenced the interference
pattern only to a comparable extent. In other words, if one does not
insist that the method used to determine which slit each photon passes
through be completely reliable, one can still detect a (degraded)
[ 2] Feynman, Richard P.; Robert B. Leighton; Matthew Sands (1965). The Feynman Lectures on Physics, Vol. 3. US: Addison-Wesley. pp. 1.1–1.8. ISBN 0201021188.
 Harrison, David (2002). "Complementarity and the Copenhagen Interpretation of Quantum Mechanics". UPSCALE. Dept. of Physics, U. of Toronto. Retrieved 2008-06-21.
 Cassidy, David (2008). "Quantum Mechanics 1925–1927: Triumph of the Copenhagen Interpretation". Werner Heisenberg. American Institute of Physics. Retrieved 2008-06-21.
 Boscá Díaz-Pintado, María C. (29–31 March 2007). "Updating the wave-particle duality". 15th UK and European Meeting on the Foundations of Physics. Leeds, UK. Retrieved 2008-06-21.
 Bartell, L. (1980). "Complementarity in the double-slit experiment: On simple realizable systems for observing intermediate particle-wave behavior". Physical Review D 21 (6): 1698. Bibcode:1980PhRvD..21.1698B. doi:10.1103/PhysRevD.21.1698.
Zeilinger, A. (1999). "Experiment and the foundations of quantum physics". Reviews of Modern Physics 71 (2): S288. Bibcode:1999RvMPS..71..288Z. doi:10.1103/RevModPhys.71.S288.
 P. Mittelstaedt; A. Prieur; R. Schieder (1987). "Unsharp particle-wave duality in a photon split-beam experiment". Foundations of Physics 17 (9): 891–903. Bibcode:1987FoPh...17..891M. doi:10.1007/BF00734319.
 D.M. Greenberger and A. Yasin, "Simultaneous wave and particle knowledge in a neutron interferometer", Physics Letters A 128, 391–4 (1988).
 Wootters, W. K.; Zurek, W. H. (1979). "Complementarity in the double-slit experiment: Quantum nonseparability and a quantitative statement of Bohr's principle" (PDF). Phys. Rev. D 19 (473–484). Bibcode:1979PhRvD..19..473W. doi:10.1103/PhysRevD.19.473. Retrieved 5 February 2014.