Jim doesn't, though. He opposes EU membership. (I reviewed his book, "In Place of Fear II", on the Big Thread).
The point Sillars makes, has always made, is that after independence, the Labour Party in Scotland has the opportunity to realign itself; to get closer to what Sillars thinks is its roots. (Because the Westminster pull is rightward, due to parties chasing swing votes in South Eastern marginals). He would then, he says, rejoin the Scottish Labour Party. He believes such a party would win a Scottish election. He makes no bones about the fact that he thinks the SNP is the vehicle for independence, but not the party he wants to see winning post independence, nor the party he thinks the electorate would gravitate towards.
He is not claiming that he thinks the SNP will do those things (or the other measures he outlines in his book).
You may disagree with him, but that's his analysis. (It's, incidentally, at the root of his 2 decade rift with Salmond, mended only as his wife was dying from Parkinsons).