Like I said earlier, last year Gscholz and I had a thread with piles of vids of MI24s taking hits and surviving, and only did I ever find 1, the above, showing a clean kill with a Manpads vs the Hind.
Read the stuff I linked earlier about missile approach warning and other defensive systems those of you asking about it - passive IR seekers missiles until recently have been a weapon that wasn't detectable really other than visually, but tech now, can detect them under many conditions, not all unfortunately, and there is a pile of different IR passive and active ECM systems used to defeat the incoming IR round. Everything from IR jammers to systems that use an active laser to flash the seeker and screw it up.
As seen from this video in the OP, the system has very, very little time to react - I figured it would have such a defensive system, as Serenity and others have said before, stuff breaks, often, or just fails to work as optimally as it does in the lab or in tests/etc. 2 or 3 seconds isn't much time for any kind of a defensive system to work - even just an alert, no pilot could have reacted quickly enough to pop out flares or activate a system manually there, just not enough time. Again, 30+ year old system too, the missile used. Imagine how much more lethal the newer stuff is, and near future manpads weapons. Pretty dangerous vs any time of low flying aircraft, but especially the helos and prop planes down low.