Also, what was helpful or constructive about "I am going to get really angry"? What, was he supposed to be scared enough to doa s he was asked?
No, he was supposed to learn that his bad behaviour was going to make someone angry.
It is ok for children to know that it will make a grown up cross if they don't do as they have been asked. At three, they are old enough to know that shoes on time is shoes on time for a reason.
I'd be wondering what she's like when you're not there
Actually, I'd say that it shows a nursery worker who is confident in her actions and methods of discipline because she knows enough about children's development in their early years to know that a firm voice telling them that their behaviour is going make someone angry, is not a bad thing.
I work in a nursery by the way, and very very rarely raise my voice at all, but our manager is the 'telling off teacher', as named by the children, and if she uses her angry voice then the children learn that their behaviour is not acceptable.