My guess is that he was used to one of the older riders that did have the driver sit lower. But - as most the current front engine riders use a full length straight thru frame design and mount the fuel tank under ther seat area - the driver ends up sitting up a bit higher.
I had an old sears rider and when I finally replaced it with a cc lt1042, I noticed that same effect. But -after a few mowing sessions - quickly got used to it and never had a problem with it wanting to tip easier.. and if I got on the side of a hill, I'd slide my big keester over on the seat a bit to help keep the tractor as stable as possible..
But, whatever make/model tractor you decide on, always get to do a test drive of it, first. Ergonomics do vary between designs and it's a bummer to end up with an unit that's mebbe too cramped for you to sit in or has a pedal placement that's a PITA to you....
Good Luck.