You can interpret that quote how ever you like...
Then afterwards, Ed calls Nicola and asks: "Do you think they bought it?"
"Yeah, you were awesome. You almost convinced me."
Then they laugh and laugh and laugh.
I tend to think that if there is going to be a SNP landslide in Scotland then a very different behind-the-scenes deal might be in the works, that of a CON-SNP government. If SNP wins 55-59 seats with a majority of the vote share in Scotland and the CON beats LAB by a solid 15+ seats then a CON-SNP deal might emerge. The basis of such an alliance would be both a Scotland Independence referendum in Scotland as well as a EU referendum in UK. CON cannot get LD to agree to a EU referendum and SNP cannot get LAB to agreed to a Scotland Independence referendum. SNP would in fact benefit from holding both referendums on the same say and would urge Scotland to vote for independence since there was a risk that UK would leave EU. CON would benefit from a rump UK where it could dominate England.
While electorally good for the long term, I don't think the Conservatives want their legacy to be the dissolution of the Union.