I don't understand what you mean. We can quibble about the details of this particular tax, but set that aside for a moment.
The best way to fight speculation is to put a tax on it. To see what I mean, imagine these 2 scenarios:
1.) There is a country without any land tax. You see a house that you can buy. You believe prices will be 10% higher within one year. Do you buy the house?
2.) There is a country with a 10% annual land tax. You see a house that you can buy. You believe prices will be 10% higher within one year. Do you buy the house?
In scenario #1 the house is a good investment.
In scenario #2, you would only buy the house if you are going to live in it, or if you can rent it out and make money off of it. In either case, in scenario #2, the house is not vacant.
A land tax forces the owners of land to use the land for productive purposes, rather than just holding it.