You're thinking too hard.
Franken never asked Sessions if he met with Russians.
Absolutely true. But Sessions decided to answer Franken by denying he met with the Russians, and he said that under oath. oops...
Franken asked that:
If the rumored dossier exists, and you found that the trump campaign had contacts with the Russians, what would you do?
HIs answer clearly was:
"I can't answer that"
Any attorney knows they can't answer a hypothetical question.
It's really that easy.
If only Sessions stopped there. Instead he expanded on his answer.
Any good lawyer advises his client to just answer the question, and not volunteer any extra information.
You would have a point if the question that Franken oddly tried to frame was about the Senate and its workings and not about trump campaign representatives.
Pity, it did not.
Without it as a basis, Sessions is free to offer any information he wishes, and framed as it was, he offered it as being called a Surrogate a time or two.
Franken, in his brilliance, then had the chance to ask for clarification.
He did not.
Therefor, there is no basis for the claim that the answer given is not actionable.