...Shouldn't hearing that from Seija of all people count as a vote of confidence?
Not really. She's saying it to be contrary to Kogasa's statement and probably also because it will upset Kagerou (who has been really cute when she's flustered in this strip). So I don't think she's going so far to be contrary to a truth she personally believes. So it's not really an extra vote of confidence over Kogasa's own statement, but more like something that should be dismissed as trolling (ie not a vote either way, just being disruptive).
She seems to have gotten it in fast enough to catch Kagerou off guard, even if Kagerou was familiar with Seija's nature. Kogasa could learn from that how to surprise people, although I don't think this Kogasa is much in for the Dark Side of Surprise.
awww..she should know that if Seija said NO means YES.
I don't think Kagerou was in on the 'Hammer conspiracy', so I doubt she's met Seija.
Y-...You think so!? How about that, what a nice person you are.♥Wakasagi and a wolf—
Heh heh hehhn!
Oh, it is to laugh!
Hum-hum-hmmm!♪Hold on, whoa! Please, get a hold of yourself, Miss Kagerou!Immmpossible...It looks to me like it's mutual for you two.♥Wuff♥H-...how could you say such a—Chuckle♡You sure do love Wakasagihime. Have you confessed to her yet?Ain't no way, no how! Mutual love?Don-...Don't be stupid! Not only is confessing embarrassing, if...if she dumped me, then I—I!!FalteringImmmpossible!