4. ACARS packets are not just received by ground stations but also by enthusiasts with scanners and freely available decoding software. There is a remote (very) chance that a radio amateur might have received and decoded some ACARS packets. I think this extremely unlikely as the packets sent appear to be different from the regular ACARS packets and may be encoded differently.
Actually, the data may indeed be logged on some enthusiast's computer. I've logged ACARS in the past, was amazed what was sent in the clear to and from my own planes, crew lists with passport and employee numbers, APU oil needs servicing and, yes automatic engine readings with lat longs and altitudes. These messages were formatted but not encoded, no harder to read than NOTAMS or WX.
Also, HFDL is easily logged thousands of miles away, there is a small user group on Yahoo. I've logged it with free software, the traffic was similar to ACARS.
Hobbyist ADS-B receivers are all over Asia, they form the basis for the networks that feed
Flightradar24.com - Live flight tracker! and
RadarBox24.com - Airspace Live . The initial transponder loss was tracked by FR24 as noted here.