I made no stipulations that the other person had to be identical to me in terms of ability. so your example. while similar. is inherently different. Their are many people who could lift something I could not. So I can easily create something that I cannot lift, depending on my ability, that another could lift, depending on their ability. A being that has an ability to perform any possible action cannot perform the action I just did. because to make an object that he cannot lift. he would have to make it impossible to lift. and if he made it impossible to lift, another could not lift it. so he would not be able to match the action i just did. so he would not be able to perform any action, so he would not fit your definition of omnipotent.
Edit: the object is not what is unable to exist, I can easily create it. the omnipotent being is.