@Clad95150
the winged person was trying to assassinate the current demon lord, and he would have probably succeeded if kail didn't recognize the spell. since even sildonia wasn't sure if the spell was disintegrate , quote '...was... that disintegrate', it's probably an extremely rare spell that only a few individuals in history could do, so demon lord and her followers probably wouldn't have recognized the spell / reacted quickly enough to it.
winged person might have also wanted to kill everyone else there too after killing the current demon lord, but since demon lord didn't die from that attack he realized he would probably lose with the current demon lord there so he retreated.
winged person might have also been there to observe Kail because Kail knowing his appearance is suspicious, now that he has seen Kail react to his spell, he might have confirmed his suspicions that Kail may have fought him in a previous timeline, and time travelled back. with the divine dragon's heart
targ explained his plan because 1. he was already the prime suspect, and the others would have probably eventually realized anyways since Kail was cleared of suspicions and 2. Targ was probably trying to distract them from his boss's disintegrate spell (which may take time to prepare since it's such a powerful attack).
@AlaskaOne
this is the manga adaptation of a light novel, this part of the story was written years ago. the artist draws one chapter a month (one raw chapter isn't translated yet), I think the artist has other professional work to do in the month though.