i think it's safe to remove presumed? in audio commentary yamada and horiguchi say about this scene being animated by ouji (lit. 'prince') and then horiguchi tells how she went to [animation] DO for her first sakkan job [which was ep5 for suzumiya in 2006] and he'd been sitting next to her still drawing douga and was so silent that she was afraid of it. no one can fit this role other than him, i suppose

if they said that then yes it's him. ouji/prince has been his nickname there for a while now due to those two