That he may have said, but he also said he had no objections to an amendment that would specifically allow and protect slavery in those territories after they became states.
That is why the slave holders bolted.
If that is why they bolted, why then did they not cease from bolting upon recieving notification that this supposed objection of theirs had been reconciled in a constitutional amendment that permitted slavery in those territories after they became states?
Too, you can only sound like a fool to characterize Lincoln as "enthusiastic" on the proposed 13th amendment.
I would tend to think that a fool would be a person who denies Lincoln's support of that amendment in clear conflict with the written record of Lincoln himself rather than the person who simply notes that record's existence and lets that record speak for itself.
But the slave holders knew that was unlikely; in any event, their investments were threatened, so they bolted.
Walt