I think the fact that there was a murmuration is important in explaining this. An individual bird flying into the ground sounds hard to believe, but in a murmuration each bird is paying attention to its seven (yes exactly seven) nearest neighbors. When flying like this, it’s more understandable that they would lose track of the position of the ground.
A thread of this nature must needs be incomplete without a posting by Icarus.
Are starlings less of a nuisance in the UK than in the US? Because, in the US, they are about as welcome as Russian Thistle. I recall hearing a story about a town in Ohio some decades ago which tried to convince them to emigrate by playing sounds of a dying starling on a loudspeaker.