A lb seems like a lot, considering that not only is a 50cm frame smaller than the 56cm reference, but it also has 4cm narrower handlebars, 2cm shorter stem and a 4cm shorter seatpost. Interestingly though the 50cm comes with a wider saddle (155mm vs 145mm).
I know you have tubeless tires, but to confirm, the bike is setup tubeless and doesn't have tubes installed? Are there any tools included/not included in the in-frame compartment?