Bigger issue is the increase in houses per household; eg one family taking up 3 houses. These aren’t rentals, or there’d still be households in them. These are holiday homes mostly sitting empty, potentially enjoying tax breaks as short stay (bnb style) holiday rentals.
That sounds plausible. Just that the graph does not show it. It does not show that the pressure on the house market is not caused by immigrants either.
As is so common at the moment, lack of individual wealth at the bottom is being blamed on a need to divide it all up and share with those who have the least instead of looking at how much of that wealth has been redistributed to the top and removed from the pool.
The graph? Of population? Not hard to see that that population living in only 1/3 of the houses would have an impact on housing availability, noting that this houses per household figure has increased - houses have increased MORE than population, they’re just not available to live in.