Its never explicitly stated as a false flag, or explicitly proven the bugs did it.
That said its generally implied that humanity was expanding into space and ended up on a bug planet and conflict broke out, after which the meteor impact happened. To that end I'd say its implied that humanity ended up on a planet, wiped out a small bug colony, and the bugs said "fuck your shit" and sent the meteor at earth.

One of the things to understand is that the earth government is not inherently evil in the movies or book. They ultimately look out to protect human interests and sending a potential civilization destroying rock at the planet will do absolutely incalculable damage to humanity (and rather unpredictable too) and for what to have a war with space bugs you have already started a conflict without any real issues? From the earth government perspective the bugs are a minor threat that their exploratory forces just demolished, they are not deeply aware/omniscient about the bugs outside of what little they do know from the fringes of human colonization.
So from a human government perspective they have no real motive to carry out a false flag, especially a false flag on the scope and scale of a giant meteor strike on earth that could potentially harm themselves.

One of the biggest problems with many of the "media literate" types is that they just write off the human government as this super government that knows all, controls all, and is almost "perfect"... except its evil, racist, fascist, and otherwise "bad". They don't really consider anything from their perspective because they have simply written then off as fascist or whatever else. So whats their motivation for doing the false flag? Evil governments do false flags, so OF COURSE this evil government will also do a false flag.