I think the remark "there are some things we can tell you and some things we can't tell you" is a fairly standard remark where multi-agency data is involved, especially if they only have a few shreds of information, some of which related to manifest items (police matters), some of which related to military radar data.
As with every incident, the only time the investigating collective have a "duty" to tell us anything is when they release a final Accident Investigation Report; and to a lesser degree if they release any initial/preliminary reports beforehand.
Anything else the SAR team mention in the meantime is put out as a matter of courtesy and we can't expect 100% accuracy. We certainly can't judge them for it.
So in summary any old tosh like "people obviously arent telling us everything" is just idiotspeak for the bewilderment of the masses.
Sure, many of us would love to step into the investigation office and see all the fragments and blind alleys they are dealing with, but seriously? If you had access to all their info at this stage, with no further clue where the aircraft ultimately arrived... wouldn't you hold off making comments until you felt you had something worthwhile to report?