An ibtidāʾī report does not suggest that the speaker lacks confidence. A trustworthy person may say “وَصَلَ الضَّيْفُ” (“The guest arrived”) with certainty but without an emphatic particle.
Conversely, adding emphasis does not automatically make a false assertion true. Emphasis is a linguistic mode of expression, while the truth of a report depends on its correspondence to reality.
The rhetorical question is therefore how much reinforcement the listener needs, not simply whether the word “إنَّ” appears.