(b) That's wrong. In this example, A has provided the promised lunches but he has delivered them late. The question is whether late performance justifies rejecting that performance and putting a stop to A's right to carry out further performance of the contract.
The common law took a strict approach to such questions, treating late performance as a breach of condition. But legislation has been enacted requiring the courts to adopt an equitable approach. Accordingly, promises in a contract should be treated as non-essential terms (warranties) unless the facts show that the parties intended otherwise. If, in the circumstances of the case, the time of performance is not intended to be of the essence, late performance does not justify terminating further performance: it only allows a claim for damages.
In the example, it is clear that the time of performance was intended to be a condition: B made it clear that the conference had a tight schedule and that lunch had to be ready on time. B would therefore be justified in terminating performance of the contract with B.