Trouble with closed doors is that in principle he might have actually told all the same people about the secret thing before swearing under oath that he didn't do the thing, and genuinely have believed there reason he gave later (IIRC that as the session was public, the question couldn't reasonably have been about the secret thing).
But we'll never know, unless someone else does a Snowden.
Congress didn't testify to Congress, Clapper did. Clapper did so in both public and private settings.
Clapper didn't tell the truth in a public setting because it was classified. Clapper (privately & immediately) informed Congress of the need for a private meeting to correct things he said in the public setting.
This would be akin to your husband asking you were the cookies are and since you noticed your son around the corner saying you don't know. Then when you son leaves you tell him they're in the top of the cabinet. Nobody is going to actually be mad except your son (that's you in this example!).
Please, don't treat me like I'm an imbecile. That's congress' job
Edit: also, that's such a shit parenting job. take the opportunity, and tell your significant other that it's not time for cookies and it'll spoil your dinner. there's no reason to lie about it. you have give a teachable moment, and you've chosen to teach it is okay to lie rather than something more valuable.
Going on TV and Clapper saying _he just made a mistake_ is really what I think you have issue with. But none of this TV statements are under oath.
If the answer to a question is classified then it is classified regardless of whether it is yes or no.
But the answer to that question being classified is objectionable, because a large proportion of the public would have taken issue with not knowing, because they would have objected to the program.
It would be like lying in a deposition in front of the board of directors and then going back in private to your friend the line manager and saying "hey, that thing I said when it really matters was a lie because I didn't want the board to find out about it."
Congress is a feckless body of government when it comes to checks and balances.