100% agree with both @Smokeycat
. Just to add another thought...I would always ask critical questions when it comes to somebody predicting future outcomes (in general). You will always need data points in order to do this with some degree of accuracy. Therefore, it‘s totally legitimate to ask: "How do you know? What data supports your claim?" Also, you would probably give a range like anywhere from 220-230 rather than a precise number (i.e. 235). Obviously parent site/weight would be the most reasonable data point to consider.
Anyway, I‘m not saying he is right or wrong, but I would challenge the thought process and arguments behind the claim.
I agree with you on your comment on inflated weights. We all know that "280 lbs Rottweiler that a distant cousin‘s friend neighbor had 47 years ago." I guess some of it is lack of knowledge, while some of it is just going for the biggest, best, fastest, greatest etc.