he outdoor guestimate won't apply if they are in a pot. maybe a really bug pot would be okay, lol. 2.5kg is a 6-8' plant i bet? so a pot that would allow that type of growth could do it.
With ambient co2 indoors, you won't get much over 50-60g/sq ft (which the "50" is 540/m^2)... maybe push 70g/sq ft? That peak is about 750g/m^2 and it would take super-yielding plants, and likely clones of one to ensure it happened. More likely this breeder is "measuring fromt he taint" aka exaggerating. But, if you can trust them, that means it's a heavy yielding plant on average. i wouldn't assume it. breeders like like you and i breathe.
but outside, as long as you aren't in a region with low DLI per day, you shuold grow monsters outside with just about any genetic that isn't an autoflower. Putting them in pots will reduce that, but you'll still get better nugs deeper down compared to indoors. If they are teh same size as indoor plants by the end of stretch, 700-800g/m^2 might be reasonable. The sun is a different animal than artificial lights. the plant is swimming in 2000ppfd from all angles, not just from the top. *assumes you aren't in a region of earth with shit sun light. There are DLI maps that will tell you the average DLI per month in your region. google for that info. 35-40 and higher will be toward upper range of yield possible.