"... Any truth?"

Nope.

There's another thread talking about controlling your watering regime to improve taste, but that's about all there is other than just good cultivation practices and proper fertilization.

And choosing varieties that strike your taste buds as being sweeter than others, though the brix measures are roughly the same in all tomatoes. But we DO differentiate among the various taste subtleties of individual tomato varieties and conclude that this one is sweet, that one is tomatoey, etc. But not everyone's taste buds conclude the same thing.

A few don't seem to cause much controversy though. For instance, most people conclude that Sungold F1 is very sweet.

If you want sweeter toms then grow sweeter varieties or sprinkle some sugar on your toms, after harvested of course.

A study was done in Japan where they measured the sugar levels (Sucrose, Glucose and Fructose) in tomatoes grown with chemical fertilization, organic (bokashi) and with chicken manure and each one also with the addition of EM (Effective Microorganisms). The results were the Chicken manure and Chicken manure with EM had the highest sugar content followed by Organic and Organic plus EM and lastly the Chemical and Chemical plus EM. Each regemen with the addition of EM had a slightly higher sugar content than without. So if you inoculate your soil with Microbial's you should get a higher sugar content with whatever type of growing method you use whether it be organic or inorganic. Ami

Ref. Nature Farming and Microbial Applications
Xu, PhD
Parr, PhD
Umemura, PhD