Vote share is highly relative and will always go up in an atmosphere where smaller parties do badly. In this case the cause is not Corbyn but is more likely to be transferred votes from the SNP, UKIP and the LDs all of which appear to have been redistributed fairly randomly. In other words its a simple function of a return to two party politics rather than an endorsement of Corbyn.
The ultimate test is the result of the election itself. Corbyn lost the election. More people wanted a Conservative Government even with a shambolic campaign and an incompetent and uncharismatic PM. Imagine what might happen in the future if the Conservatives just ran an average campaign with a leader who had just a bit of charisma?
Instead of trying to twist the statistics around to suit some kind of Corbyn praising narrative it is a better idea to instead reflect on what went well and what went badly. Considering the quality of Corbyn’s campaign (great), the Tories campaign (terrible) and the circumstances this very much looks like peak Corbyn. As an example imagine if he was running against Ruth Davidson in 2022.
If the Labour party want to improve on their performance they need to first stop wallowing in that good feeling that comes from exceeded expectations, move on from their state of denial (they lost) and come up with a long term plan to turn this loss into a win in the future. Corbyn should be gradually eased out, potentially he could become some kind of party grandee or advisor and someone who can capture the center ground a bit better should replace him such as Mr Ummuna or Sadiq Khan.