Agreed, but I believe Voyager is 18.5 light hours away, not 22. The article says it is 20 billion km away which is 18.5 light hours.
However the article also states signals take 22 hours to reach the spacecraft. Do radio waves travel slower than the speed of light even in the vacuum of space? I assume the waves do not spend the extra 3.5 hours in Earth's atmosphere!
I think it's because space isn't a perfect vacuum. The interstellar medium is a mix of gas and dust that slow down and weaken the signal. That effect is known as dispersion.
With that said, it seems like the article might be inaccurate. That discrepancy seems too large to be explained by dispersion. I'm not an expert though.
edit:
I think the author got Voyager 1's distance mixed up with Voyager 2. Voyager 1 is ~22 (21.6) light hours away.
Voyager 2 was launched first but on a less direct trajectory out of the system which allowed it to visit Uranus and Neptune. Voyager 1 is going much faster
There is an effect called dispersion, which causes different frequencies of electromagnetic radiation to travel through a medium at different speeds (lower frequencies => slower).
It's strong enough to be noticeable in the case of pulsars (but probably insignificant inside the solar system).
Don't confused TTFB with message transport time. With a low bandwidth link, throughput becomes part of latency. Probably not 3.5 hours, but some fraction of that.
However the article also states signals take 22 hours to reach the spacecraft. Do radio waves travel slower than the speed of light even in the vacuum of space? I assume the waves do not spend the extra 3.5 hours in Earth's atmosphere!