He carried on eating sahoor even though he could hear the adhaan from a TV channel
The fasting person has to refrain from eating and drinking when dawn breaks, because Allah says (interpretation of the meaning): “and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)” [al-Baqarah 2:187]. If a person is certain that the true dawn has broken, he has to stop eating and drinking, and if there is any food in his mouth he has to spit it out; if he does not do that then his fast is spoiled.
But if a person is not certain whether dawn has broken, he may carry on eating until he is certain. The same applies if he knows that the muezzin gave the call to prayer ahead of time, or he is not certain whether he gives the call at the exact time or before it. Then he may continue eating until he is certain, but it is better for him to stop eating as soon as he hears the adhaan.
Adhaans on the television, radio or satellite channels may be ahead of or behind the adhaan of the place where one is, based on differences in the time of Fajr from one country to another.
Based on that, your brother does not have to do anything because he was not certain that dawn had broken and he did not hear any adhaan near him to indicate that it had broken.
For more information please see the answer to question no. 66202
And Allah knows best.