It is a fact that Ariyas declare their attainment in order to teach and spread the correct Dhamma. Otherwise Puredhamma.net would not exist, and we would not be here on this Forum.
This training rule must be referring to those, whatever their attainments be, who do so with selfish intentions, whatever those intentions be.
Then I looked up and found the following:
The training rule on telling truthfully
(I hope I succeeded in forwarding the link)
Apparently not.
What is spoken of at the end is uttarimanussadhammassa (superhuman qualities). The bhikkhus were truthful,they tell the Buddha so, since Bhikkhus and even lay people know full well the very grave consequences of claiming falsely (even of a higher attainment they know they have not reached at that point).