You're looking at the median HOUSEHOLD income. So on average the wages of two people, median income is a bit below half of that at 31k (pre tax I think).
If you look at Table C-1 in parent's source, it has median post-tax household income at 65K which is a much more reasonable number. We're incredibly wealthy, a per-person median income of 19K doesn't pass the sniff test. Keep in mind taxes are much lower at the lower end of the income spectrum as well. If you're married and making the median income, your overall federal tax rate is only going to be about 15%.
If you’re married and making the median household income, your overall federal tax rate will likely be significantly lower than 15%. You’ll be in the 15% bracket, but roughly half your income would be taxed at 0%.