I don't think Tenet did that. He reported that he couldn't prove it one way or the other, similar to what Cheney says.
Its the unnamed CIA sources who allegedly say it didn't happen, arisen again in teh 9/11 Commission report.
You are correct. Tenet didn't 'shoot down' the story. The reason he couldn't confirm the meeting was an obvious one- the intel was obtained by a Czech agent, not a CIA agent, much as the intel for the attempted purchase of uranium in Africa came from non-CIA sources, namely, the UK's intelligence service. The CIA director would be stupid to sign off on intel his agency had no hand in collecting and cannot independently verify... it's risky enough to be held responsible for his own agency's squabbling factions of political appointees and hacks.