When someone weight trains with such intensity and relative heavy poundage for decades, understand that there's more to his or her bodyweight at that point than just muscular weight. The skeletal structure and connective tissues of the body also develop and add pounds. Not to mention that the lean tissue is very marble-free and thick. Like forged steel.
No one here would believe I am 290 pounds, but I am. And no, I am not bodybuilder lean, but I do hold such bodyweight very well. No drugs either, by the way. However, I have been lifting with total passion for about 26 years, so ... there ya go.
In the same way, Dorian doesn't appear in person (ate lunch with him last Summer) as a 265-pounder, but I have zero trouble believing he is.