Also, all the other Labour candidates have been saying that Corbyn is too left wing and that they need to move further right as a party, which considering they're already centre-right and got demolished in the election, including a drastic loss of support to a left wing party in Scotland, is pretty odd to me.
Labour basing their swings off of Scotland would be a bit weird because the SNP are also a nationalist party, unless we can summon the Owlbread to clear things up I bet it's because Scots didn't feel Scottish Labour was Scottish, not that Scottish Labour wasn't left wing enough.
Also what you talking about, Labour's centre-left; where are labour candidates saying labour must swing right? That's not rhetorical, I'm actually intrigued
Scotland usually polls as being significantly (30% last I checked) more inclined to left wing politics than England does, so the SNP success is as much a result of being much further left wing than Labour as it is being Scottish. A surprising amount of SNP voters are anti-independence, weird as that may be. Labour are being referred to as Tories by a large chunk of SNP voters in Scotland as well as the Conservatives these days, only distinguishing between them with the prefixes Red and Blue.
As for Labour being centre-right, it's been so roughly since Blair was first elected (basically since New Labour became a thing). It's been opposed to most left wing policies like nationalisation of public transport, water, electricity and so on (notably Blair stood on a platform that was in favour of nationalising the railways but then reneged on it), in favour of deregulating things like the banking industry, cuts to public services and support agencies for the poor, etc etc. They actually have very few major policy distinctions with the Conservatives these days.
There's a political graph calculator that was floating around the internet about the time of the independence referendum that scaled you according to authoritarianism/libertarianism and left/right based on your stance compared to the political parties on policy. Labour, Lib-Dems, Conservatives all sat in the centre-right, with the cons being furthest right, but mostly differing on the auth/lib scale. UKIP, BNP etc. sat on the farther right, SNP was centre-left and Greens were far-ish left.
https://www.politicalcompass.org/uk2015 It's largely based on economic policy determining right/left axis, personal freedoms auth/lib axis, and a few of the more buzzword marxist/fascist idealogical concepts.
Essentially while Labour is the most left wing of the major parties in Britain aside from the SNP, they are still quite heavily to the right in the grand scheme of things, as are the Lib-Dems.