Eh, it's kind of hard to say because the statement "10% of all civilizations" isn't really meaningful as it seems to rest on an idea of a "civilization" as a countable, concrete thing, such that you might be able to go to an island and proclaim there to have been four different civilizations there. But a civilization is a retroactive construct, a way of dividing up the raw material of history and archaeology to make it legible and comprehensible, and this division is not objective or fixed. To give an easy example, one might talk about "Greek civilization" and "Roman civilization" but another "Greco-Roman" civilisation, and still another might make subdivisions for, say, the civilization of Roman Egypt. You can't just add up the number of civilizations discovered and get a simple number, and the fact that they are doing so is a sign that the, shockingly, the ancient alien program might be a bit crankish.

For the claim behind the words though, it is certainly true that the uncovered archaeological record it pitifully small compared to the theoretical sum of knowledge. Often, this is much more in terms of details than at the level of "civilization", as there are plenty of places where you can do a "culture history" (the disfavored approach of using archaeology to construct a succession of cultures that have existed in a particular spot) without the material to know much meaningful, but even in areas with a great deal of scholarly attention (like the classical Mediterranean) one can easily say that the amount of work done is far less than 10% of the amount to be done.

Of course the purpose of this doubt mongering is so they can say even the archaeologists don't know anything so there is no reason it can't be aliens! The problem is that this conflates the idea that archaeologists don't have perfect detailed knowledge of a place in time--often if not always true--with archaeologists not having a pretty good jist. To give an example, the Neolithic monument if Gobekli Tepe is much beloved of cranks like Graham Hancock and Joe Rogan because they can point to it and say, see, archeologists act smart but here they are completely blindsided by this discovery! The earliest temple! A massive monumental complex from before civilization! And there is some truth there, it seems to predate agriculture in the region, it is quite large and quite old, and may be the "earliest" something it other yet found. But does that mean that it was a shock, overturning long held assumptions about civilization, showing that truly our ideas are mistaken, scholars are all just blind men in the dark, and Atlantis was located on Antarctica which used to be in the middle Atlantic? Well, no, as a matter of fact Gobekli Tepe serves to reconfirm, strengthen even, very long standing narratives about the development of complex cultures in the region. It dates more or less exactly to the period and the place that James Henry Breasted in 1915 had identified as more or less the time and the place where things like agriculture, large settlements, and monumental structures came into being. Finding the "oldest monumental temple" in 10000 BCE southern Turkey is more or less the opposite of shocking, paradigm destroying discovery.

What History Channel and its ilk do is exploit a conflation between a specific sort of ignorance (we didn't know there was a big monument there) and a general ignorance (it is shocking and inexplicable that there was a big monument there).