I submitted this link too but removed it as a duplicate, and it's really a category error from the Liberland people. They are writing from their perspective - they are a sovereign state with citizens, and the raid by Croatian authorities is a literal invasion. However, from the point of view of Croatia, international law, and everyone normal, they are squatters who are illegally constructing buildings on land controlled by Croatia.

A lot of the HN commentators sympathetic to Liberland would have a fit if a group of Mexicans set up an enclave in Texas and started constructing buildings. These hypothetical Mexicans might have their own spin on the treaty of Guadalupe Hidalgo which they spun out of reading too much Wikipedia, and their claims are just as valid as Liberland's.

There are a lot of neocolonial echos in the Liberland post too:

Liberland has the ability to bring significant investment, jobs and tourism to this economically depressed region.

Yeah sure, you can do a lot within the framework of existing Croatian law to bring investment, there's no need to set up a LARP country on a floodplain to do so.