I love body language theories, and you are right.
He was scared, all Argies were scared, nervous and under huge pressure.
But you could have also felt: if they concede, they will explode (in a negative way), plus they will be clueless and give up.
I know, Messi's mental strength will suffer even more after this.
But, as Barca's fan, I am afraid: next year CL's quarters: when we will be 1 goal down, we all know deep inside what Messi will do...
He will sulk and give up even more than now.
That's a harsh reality.
From now on, he will probably deliver in low pressure La Liga games and CL group stage.
And whenever a pressure will be on, and if we will be losing, don't expect too much from broken Messi.
Some new guys, like Coutinho, will have to try do something in the 80th minute at 0:1.
All big teams KNOW how to stop Messi in this moment.
And now, even worse, when we will be losing in a CL, he will totally disappear.
I know that this post will sound harsh, but mentally, he received too many kicks and knocks and we have to be prepared for mentally less strong Messi when things will go bad.