No hun, not even close. whatever you call it, the existance of limits does not constitute topping. What makes you think the sub's limits are by default tighter than the dom's?
No... topping from the bottom is about who controls how play proceeds once it begins.
Discussing limits, scenes, rules... is about communication and setting expectations. Thereafter, so long as those expectations are being kept, if the dom chooses the when, how, how often, how much, then he is dominating.
If you are telling him during the scene to hit you harder, tie you tighter, when to do this or that, well, that's topping. If you throw a tantrum to change how the scene proceeds, act the brat to modify his behavior, disobey on purpose (outside of a roleplay) to force a punishment, those are acts of topping.
Your limits are valid concerns... so don't give them up if someone suggests having them is topping.