You know what, massive shout-out to our TL for this series. No begging, no advertising, no complaining, just high quality TLs at a good pace. What a legend.
They didn't recognize each other before because they never saw each other's face. Seriously, look back through all the previous chapters where they were both at college and in the same room; at no point did either of them have an unobstructed line of sight to the other's face. There's even one time when Urumin briefly mistook another guy for Kimiya, who ironically was further away from her in the opposite direction and thus she couldn't hear him talking to his friend.