Firstly, my claim that they say this is evidenced by the link. I did not assert it as historic fact that this thing works, just that this is what they say. The words "Selling point" and "proposed" are in that sentence for a reason: it's not actual yet. But if you think it's a deliberate fraud, then say so.
Secondly: Although the final proof of it is in the full scale aircraft for sure, a lot can be done with software modelling (1) and wind tunnels these days. And with the scale model that just flew, to be followed by "checking the actual performance that was demonstrated against what our models predicted, and how we expected it to fly." (2)
Thirdly, I point you to other "quieter supersonic" aircraft work in progress, the X-59. Some of their evidence-gathering process is detailed at the Wikipedia link, "development" section. (3)
It will be interesting to see how these work out; but if they do not, then it's a failure of modelling and design, not because they missed the directly obvious. But if you are an aerospace engineer and know more about this subfield, then say so.
1) "Boom has perfected its aircraft’s efficient, aerodynamic design using computational fluid dynamics, which “is basically a digital wind tunnel"."
A sonic boom is not necessary when moving faster than sound, the Busemann biplane resolves that completely.
There's been considerable work on sonic boom mitigation for many decades. Boom's long nose, flat underside, top engine, small wingspan delta wings are all designs expected to mitigate a sonic boom. Let's see if it works in practice.
How have they demonstrated that they know how to cause quieter sonic booms?