not gonna lie I thought they already knew they have feelings for Otaku kun, dammit, still such a sweet moment, thanks author-san and to the TL team I love yah guyz.
I think its fine. Its not like the motifs don't represent aspects of each girl well. Seo is an awkward guy and I don't think its reasonable to expect any gifts to be able to fully describe a person. The notes he wrote likely went into a lot more detail even if the author didn't want to tell us what was written. I think the result was very in line with his character.
I'm not sure if I think it's fine, especially in Amane's case considering that her cool persona is mostly the result of her suppressing her real emotions and opinions for fear of not being understood. If you think the real you is different from your public persona (which Amane does), it can feel pretty alienating if someone identifies you with it.
Also, given where he trailed off in the manga, I think the context of the notes was him showing appreciation for their relationship rather than anything specific about each person.