Yes, "just" in the sentence "I just went for a run" can have both meanings, depending on the context:
1. A short time ago:
* It means you went for a run very recently.
* Example: "I just went for a run, so I'm still a little tired."
2. Only (nothing else):
* It means the run is the only thing you did, emphasizing simplicity or exclusivity.
* Example: "I just went for a run; I didn’t do any other exercise."
Context determines which meaning applies. If the focus is on time, it means "a short time ago." If the focus is on activity, it means "only."