Ruby and Dorothy were pretty cute, but there really weren’t any “seeds” (Adam’s words) in S3a (other than the sleeping curse from which Hook’s dad supposedly awoke via TLK). At least in the case of Ruby and Dorothy, they had at least met prior to Dorothy falling under the sleeping curse (unlike in the case of Hook’s dad and the nurse); yet, it’s really quite unbelievable when any couple falls in love so quickly. Sure, each person can be attracted to the other, but true love at first sight? Come on!
I think the other seed Adam meant was that Ruby felt the need to go off an find her people (which is a heavy handed and weird way of saying she’s gonna be gay). But yeah, I agree with the super rushed nature of this relationship, even if they did have some heartfelt moments