i don't know about the author/teacher, but the information in the video is correct. adhan should not be sung, nor elongated unncessarily and singing is also not allowed - this is commonly mentioned in fiqh works.
He may well be a salafi but he might still be correct on the point regarding over elongation. Reciters like Sudais etc actually do this when they're reciting Quran too, in order to show off their voice, meaning certain rules which are Sunnah are not followed on occasion. I was wondering if it's the same phenomenon here- or whether the guy in the video is just flat out wrong.
Didn't see this video but I've seen another video from this channel saying the division of the Qur'an Sharif into 30 juz is an innovation. Gave me pseudo-salafi vibes.
This video mentions common mistakes in the reading of the azaan, and I've definitely heard many of them. However, if you see from minute 8.30 onwards, he speaks about over elongation of words. How accurate is his explanation of this specific type of mistake? Because I've never heard any azaan that doesn't, for example, have elongation of over 6 harakaat in "حَيَّ عَلَى ٱلصَّلَاةِ", even for those usually famed for accuracy in recitation of the Quran, such as Shaykh Al Hussary. Is the video wrong (I don't know who this guy is) on this point or...?