Alone by himself? Scouting/spying probably and got caught. Looks like drones aren't all that available around the clock either or maybe planting devices inside Indian side.
One lone soldier could only mean one or a combination of the following.
1. Guys positioned there are very unprofessional and unbelievably disorganised - unlikely a single person gets sent out for any "conventional" task.
2. The soldier was captured by Indians on PLA side - unlikely since that would require them to have ambushed a small group or caught one guy alone somehow which is just not going to happen unless he went awol. Also would have become a pretty big mess if that's happened.
3. Scout observing Indian positions and activities but there are so many cheap drones that can do that job cheaper and more effectively. Literally a $50 drone with a $100 camera can do it better, faster, and for longer.
4. Defector - actually more believable than the first three.
5. Guy was sent into the Indian side, maybe with one other person. Reasons could be observation since small drones flying into the other's side would be easily detected and recognised as escalation. HALE/MALE drones might be considered too expensive to have running around the clock or for trivial observation tasks which the Indians are doing to China as well no doubt since they knew how unguarded the south of lake was half a year ago. Maybe they went in not just to spy on Indian positions but to drop some monitoring devices?
Just wondering alone innocently into the Indian side is the official BS story. Expect the guy to get tortured if not a defector. They'll want to know what he was doing
PLA should be learning lessons! Second time it's happened?
This Ladakh situation is actually pretty perfect for playing around with drones and learning tactics, adapting the technology to real life problems.