Yes, it's colonisation. It's also even more authoritarian than that, as the language they advocate was created by an extremely tiny group in academia where queer theory rules.
The first paragraph in the guide explains to us that language can deconstruct the power structures which cause poverty.
If that were true, we would have gotten rid of poverty a long time ago.
But language can obfuscate and make discussing something much harder and more difficult, and the changes they propose do obfuscate language, even where they don't introduce impossibly contradictions etc.
As an example of some of that, the guide argues that 'poor people' is not a statement that should be used as 'poor' has all sorts of connotations. But the alternatives are longer academic sentences which would cause confusion in many and would make communication much more difficult.