It doesn't tell you that though. It might tell you that but you don't have enough information to be able to say and you are effectively saying there is no such thing as a swing voter which we know to be false. 1960s to 1980s there was far more party loyalty with about 20% of people reporting that they voted for a different party from one election to the next but this has been steadily increasing and is now in the 30-40% range every election.
Blair/Cameron were successful because they could win votes from the other side. Boris managed it from a combination of Brexit and Corbyn.