Sure, it is reductive but I also get what the image is referring to and don't think we have to be too literal about it. It's saying the spirit of that tax (ie. taxing the ultra wealthy) is how Mamdani is going about balancing the budget - while invoking a very recognizable billionaire to drive the point home. I read it more as using Taylor Swift as an example rather than insinuating her taxes, or the secondary estate tax in general, would be enough to balance the budget on their own.
Many hot takes are like this. They're meant to capture your attention, and while they may not be literally true on their own, the good ones have a reasonable conceptual foundation.