A construction company cannot steal an engineering company's design for a road or building just because they have the concrete and steel to be able to build it.
The difference here also is that Lego have made their instructions freely available to you, Cada and Bruno have not.
This is because to build a Lego set from Lego instructions, you would need to own all of the pieces to do so, as manufactured by Lego.
This is a clear difference, as doing so would require a person to have already spent a significant amount of money to acquire those pieces from Lego, whether in the short or long term.
Lego do not make their parts lists and instructions free out of altruism. To assume so would be naive.
In essence, Lego are happy for you to have access to their instructions to build for free, should you have the pieces, as they can afford to because you must have already bought the pieces from them, and doing so keeps you engaged with the brand and product.
In this case however, one would be using Lego pieces to build a Cada design, thereby circumventing any measure by which Cada can make any money from this endeavour.