Blaming others is common in most disputes that come to mediation.
There is nothing new about this, and an enchanting old example from The Book of Genesis was read out during Mass today in many Christian churches:
The Lord God … asked ‘Have you been eating of the tree I forbade you to eat?’
The man replied, ‘It was the woman you put with me; she gave me the fruit, and I ate it.’
Then the Lord God asked the woman, ‘What is this you have done?’
The woman replied, ‘The serpent tempted me and I ate.’
So Adam blames Eve. Adam also blames God (for putting Eve with him). And Eve blames the serpent.
In mediation, parties are encouraged not to dwell on blame, which tends to keep them stuck in the dispute and in the past, but to find a way of moving forward to a solution that works for them.