what Onlyme is saying is that tyson is one of those mofos that are naturally thick, dense and strong as hell. this is exactly what cus d'amato saw when he proclaimed that a 13 year old complete novice was going to be the hw champion of the world.
as keith said, tyson built his massive neck without barbells and dumbells, just bridging exercises with body weight and occasional high rep shrugs with a weight that your average bber would do db curls with.
the current version of tyson (let's say from ettienne on) probably does do weights like bench press. looking at his thicker build in recent times it is probably true, but the reality is that it hasn't helped him to be a better fighter.
he has lost much of his movement, agilty and speed, but that has more to do with age and lack of motivation than any possible weight training he is doing.
keith is also correct about how boxers were trained back then.
i grew up in boxing gyms and people here wouldn't believe how archaic PROFESSIONAL boxing trainers continue to be.
running, running and more running including sprints and interval training.
skipping, skipping and more skipping includin sprints and interval skipping.
lots of heavy bag, speed ball, floor to ceiling, focus mits, basically anything capable of being hit.
shadow
pushups, situps ad nauseum...
partner drills
sparring
repeat
EVERYONE was dead against any form of weight training and anyone with an open mind would advocate light weights only. i was told if i had any energy left over from the above protocol i obviously wasn't training hard enough. 'do more running son.'
holyfield was considered to be committing heracy when news got out that he was training with some bber guy (haney), but he did a lot to dispell the myths associated with it.
ironically enough he managed to out muscle one of the strongest fighters of all time (tyson) and made believers out of a few of these naysayers.