Poland has been a vocal opponent of both the European Union and Russian authorities, while the latter are not being described in any other terms than an “imminent threat from the east.” Their overseas masters whom Warsaw relies on to decide its geopolitical policies won’t prevent Poland from taking reckless steps upon the European stage, as those go in line with their “hardline policies”.
The disinformation message - like many others - appeared after the meeting between President of Poland Andrzej Duda and US President Donald Trump and the signing of an agreement which will increase the number of US rotational military forces of Poland. The United States and Poland are NATO allies. Poland is a sovereign state, which determines its security and defence policy. Narrative about Poland being a 'vassal' of the US is one of the most common, recurring messages of pro-Kremlin outlets. Other countries are often claimed to be the American 'vassal', too, without any evidence. See further examples here.