Is this the right or wrong way to punish a child?

My boyfriend has a 4 year old girl. This evening at dinner time, she would not sit still at her table. She ate only when told constantly to eat. Several times my boyfriend put her back to the correct seated position and instructed her not to move around and eat. When she did not listen, he told her that if she did not hold still and eat, she could not play after dinner. After dinner, he told her she could not play, so she went into her room and got her books and had a grand old time playing. After she had been put to bed, I pointed out the perceived error in his punishment technique. First off, he did not say what she should do instead of not playing for example, "You will not play, you will sit quietly for 10 minutes." Therefore reading her books, something she enjoyed to do, was fair game. My argument is that he should not have let her read her books. I say this because that is something she enjoys to do, Therefore during the period where she was being "punished" (by not playing) she just went and did something else she enjoyed doing, therefore diminishing the effectiveness of the punishment. She was able to do something she enjoyed doing (reading) even though she did not do what she was suppose to do (hold still while eating). My boyfriend argues that he will never tell her that she cannot read her books because he wants her to read. I think she should read, and should be allowed to read, but she reads with her father every night before bed. Therefore she should not be allowed to read when she is being punished because hes just letting her trade punishment for something else she likes to do. So what do you think? Is it wrong to use no access to fun things, even if it is reading, as a punishment? If he uses access to reading along with other fun things as a punish-er, will she stop reading? He argues that even if she ociates reading with punishment, even if his punishments become ineffective because she is allowed to read when shes being "punished" thats fine because he would rather her read than supposedly not listen or do what he is asking her to do.