I don't think the English translators would have made such a mistake as this, I believe it was an intelligent interpretation.
As regulars of this forum know all too well, I am not exactly a great fan of the English translations of the original French comics - but maybe my own leave a little to be desired.
A more direct translation of that panel would be:
TINTIN: It's incredible!... But what would he have needed this notebook for?...
MINISTER: In order to recognise without fail the people whom the real professor Alembick frequented... For here is a photograph which our police also obtained and which will give you the key to the puzzle...
Nowhere in this panel, in the original French, is the notebook mentioned as being used by a group of people. It was simply for the use of a single individual, Alfred.
Another clue regarding the use and purpose of the notebook is the heavy text 'liquidated' and 'don't trust him'
Well, I think that those are still for Alfred's benefit. In the case of Kaviarovitch it informs him that that man has been liquidated and thus not someone he needs to look out for, whereas Tintin is someone to be wary of.
As an aside I think it's interesting that the English translators got rid of the name Nestor, probably as Nestor the butler had appeared by then in the series. Also I note the date on the twin's photo is changed from 1934 to 1947 which would place the story after WWII.
Here's another one:
in the original black-and-white edition of "Sceptre" published before the war, the minister tells Tintin that the photo was found at Musstler's place;
in the post-war colour edition he does not mention where the police got the photo;
the English translation of the same colour edition also mentions "Musstler's house". Another liberty on their part, or had they also read the black-and-white version?