As reluctant as I am to side with Machiavelli over LJ, I'm afraid I have to agree that the mere use of the formula "for not having committed the act" in the announcement of the verdict does not indicate whether the acquittal is under 530.1 or 530.2. This will be specified only in the motivation document (since no mention was made in the announcement) .
To think that the above-mentioned formula distinguishes between 530.1 and 530.2 is a category error. According to my understanding, there are two independent "axes" of classification for acquittal verdicts. On the horizontal axis (let's say), you have the categories "For not having committed the act" (i.e. someone else did it), "Because the act does not exist" (e.g. if the victim turned out to be still alive), "Because the act does not constitute a crime" (e.g. perhaps if they killed the victim in self-defense), etc. Then, separately, on the vertical axis, you have 530.1 (finding of innocence) and 530.2 (insufficiency or contradictoriness of evidence of guilt). The wording of the announcement only served to mark place of the ruling on the horizontal axis, without saying anything about the vertical. The announcement of "For not having committed the act" meant that whatever reasonable doubt the court had (regardless of whether or not it was of a sufficient level to justify a 530.1 finding) had to do with whether Knox and Sollecito were responsible for Meredith's murder as opposed to someone else, not with e.g. whether Meredith was murdered in the first place, or whether she was killed with homicidal intent.
In fact, my suspicion is that the upholding of the Lumumba slander charge is a signal that this will turn out to be a 530.2 acquittal.
I also argued along these lines, but I see now that almost all Italian newspapers take it for granted that it was 530.1.
Is it just copycat journalism?
Logically, however, I can't imagine that the judges can deduce with absolute certainty that they did not commit it.
That would be even more difficult than Massei's effort to deduce that they did.