Qiraat

Reciting from different surahs in salaah

Q: In one musjid, the Imam Saheb read in the first rakaat of Fajr Salaah from the middle of Surah Tahreem,

يا أيها الذين آمنوا قوا أنفسكم و اهليكم

till the end of the Surah. Then in the second rakaat he read a different surah. Is there any reason for doing so? Would it not be better to start at the beginning of the Surah, read 2 pages, then in the second rakaat finish off the Surah?