The pictures aren't clear enough to see inside the boot to the actual joint.
Its possible they pulled it back enough to inspect and saw critical damage or maybe they just made the assumption based on how dry/dirty everything is.
When a boot tears, it makes a god-awful mess.
They also have to worry about liability.
-I have been in situations where you explain to the customer all the downsides and yet they insist on trying to economize and when it doesn't work out, they still get upset (even though you warned them, repeatedly) and it causes a lot of bad blood and lost profits and no one ends up being happy.
Doing your own work eliminates that aspect of repairs.
Also helps you to appreciate their perspective, when the attempt doesn't work out.