I looked a bit, and the numbers really don't match my expectations, I'm pretty sure they're not counting the same things. I found one paper that compares the US and Germany and they got a lifetime prevalence of homelesness of 6.2% in the US and 2.4% in Germany (https://sci-hub.se/https://doi.org/10.1002/casp.724).
I know it's dangerous to rely on my own expectations and biases here, but the numbers are too far off for me. And I think it is very likely that the criteria for homelesness vary greatly between countries.