I have heard this phrase several times recently and I hope not, because there are so many ways to sit that are comfortable and beneficial! (Not to mention, many people are confined to sitting due to mobility challenges.)
Here are seated positions that I have found helpful, and you can learn more in my book, Circles of Healing.
Sitting on an exercise ball, or on an exercise ball resting in a frame (available from Gaia) for stability
Sitting on a yoga bolster
Sitting and meditating, perhaps in a yogic position or modified pose
Sitting on a chair with legs resting on a large exercise ball
Sitting with a bolster behind your upper spine (or one or two smaller balls) to open your chest
Sitting with legs outstretched and smaller balls resting under hamstrings or calves (helpful for sciatica)
Sitting in car, plane, bus, subway with balls behind your lower back if you are experiencing discomfort there
Sitting with a foam roller supporting and stretching your spine
Sitting with a ball behind your neck to help elongate your neck and reduce tension around the base of your skull
Sitting and using hands to balance and calm yourself
Of course, sitting on a yoga mat or on the earth and doing gentle stretches and breathing is healing, as well as all the subtleties of how and who you sit with! An animal, a loved one, listening to beautiful music, smelling healing scents and more.
That said, due to our high tech age, sitting still may be the new smoking, so when and if possible do less of it, and more dancing, swimming, walking, yoga, working out, martial arts, etc.
If you must sit, and for those who have no choice, do some seated stretches along with coordinated breathing. Chair yoga is increasingly popular. Judy Kyle, former Murrieta Hot Springs yoga instructor offers a great chair yoga class in Murrieta, Ca, in which she incorporates stretchy bands and other props.
Or sit back to back with a partner and help each other stretch and move your energy, even if you can't move your whole body. In any position you can build your center or core strength and awareness. Strong core = strong back = hopefully less need to sit!
My final observation on this subject is that many people in the world spend too much time standing, either because they push themselves or their work demands it. If this is the case, please sit and when you do take the opportunity to stretch and open and relax, without collapsing and compressing your spine and internal organs. Allow your spine to lengthen, your sternum to lift and your shoulder blade area to widen. Internally scan yourself, and relax as needed.
May you find balance and peace, in whatever position you find yourself!