In the mind of a collectivist like Trump, it makes sense to think of America as an entity capable of being ripped off. He's not thinking of the government, specifically, or the people. It's all just one big blob.

Now, I do think he has a very poor understanding of trade, but I can also make a charitable argument out of his position. He's clearly objecting strongly to all of the protectionist non-tariff trade barriers that other countries erect, largely to be competitive against American producers. We're seeing it over and over in the news right now, as foreign leaders make their fake "0 tariff" offers that the media runs with.

In that context, it's both American businesses and the government that are being "ripped off". Although, that's not the phrase I would use. The businesses are being ripped off, by limiting their access to markets in ways their counterparts aren't restricted from the US. The Feds are being ripped off because they've been duped into adopting lower tariffs, by foreign leaders pretending to have similarly low trade barriers, which leads to less revenue than symmetrical trade restrictions would.

Of course, you're right that the people really being ripped off are all the regular peaceful people being expropriated by the state (doesn't matter which nation's).