There are two reasons I can think of off the top of my head why that should not have been a problem:
1. Congressional committees that handle classified information can use closed-door sessions to hear these kinds of answers. There was no need for Clapper to lie.
2. Clapper also took an oath to uphold the constitution, before any other more specific oaths. It is difficult to see how lying to Congress fulfills this oath.
At best your argument rests on whether Wyden knew the answer and the common law argument that no answer could then be perjury. But there was no reason for Clapper to lie to a committee of the Congress.
1. Congressional committees that handle classified information can use closed-door sessions to hear these kinds of answers. There was no need for Clapper to lie.
2. Clapper also took an oath to uphold the constitution, before any other more specific oaths. It is difficult to see how lying to Congress fulfills this oath.
At best your argument rests on whether Wyden knew the answer and the common law argument that no answer could then be perjury. But there was no reason for Clapper to lie to a committee of the Congress.