This is my understanding too. I have a Kurzweil K2500 keyboard from around 1999 that has a bunch of the alternate tunings, including three from that era. The Bach-era tunings weren't what we know of as "equal temperament." Truly equal temperament didn't come around until well after Beethoven was dead. I've always interpreted the "Well-Tempered" in Bach's title to mean that he was brining out the strength of each key. Some of those keys sound really "out of tune" to modern ears -- I have a friend with perfect pitch who legit can't listen to them.

Owen Jorgensen's "Tuning the Historical Temperaments by Ear" is good bedtime reading on this topic, if you have a couple hundred bucks burning a hole in your pocket. https://www.amazon.com/Tuning-historical-temperaments-ear-ei...