Its down to kit design and model type, some kits utilise a false keel as also being the real keel, some kits start with adding the real keel to the false keel then adding the frames/planking.
In our instance as you know, the real keel is added to the false keel after the model has been planked, which is what the kit designer/manufacturer Artesania Latina recommend.

In our instance the real keel is 6mm wide whilst the false keel is 4mm wide, so there is an immediate centering alignment of the real keel to overcome, which is why the build format is as it is, with the real keel being added after the hull has been planked and a real keel central alignment slot made.

There's nothing stopping you from stepping outside of the instructions and doing your own thing, but should your build then go wrong, your then own or on the reliance of others to sort out the problem, a novice should stick with the intended build which in theory has been worked out to avoid pitfalls.