Hi, Apple,
Participial constructions can be used to refer to previous, simultaneous, or subsequent actions or states.
When simultaneous, as is the case with your sentences:
- Jack stood there alone, looking surprised.
- Jack looked surprised, standing there alone.
we can have:
A) two actions (the main one will be the one we use the tensed verb for and the secondary one, the one in participle form):
3. Jack stared at her, wondering what to do next.
B) two states, or an action and a state (usually, we will keep the main verb for the action and reserve the participle for the state that provides background information). In your sentence, although "standing" describes a state of stillness, that is, a stationary position, it is in fact an action verb, while "looking" is a stative verb, so the rule I just came up with applies:
1. Jack stood there alone, looking surprised (with a look of surprise on his face).
We can also have a state verb as the main verb followed by an action verb, but without a comma — the action verb will account for the state, for example:
4. Jack looked ridiculous standing there alone.