The excerpt merely says Tryshulyakov claimed to have found a way to absorb radar - and Tryshulyakov didn't give any details specific enough to allow Solzhenitsyn and colleagues to build a working sample, or even theorize how this would work.
I don't think you can call that an "invention of stealth technology". Tryshulyakov came up with an interesting theory, but didn't have a way to put it into practice. It would have required a series of experiments to find a material combination that worked, and evidently Tryshulyakov didn't get to that stage.
After the invention of radar, it'd be obvious to anyone working in this field that there should be a way to make aircraft invisible to radar, by either deflecting or absorbing the radar energy. A bunch of layers of partially-reflective materials is an obvious way to do this. So it's not surprising to me that an inventive Russian would think of this.
from Wikipedia:
The earliest forms of stealth coating were the materials called
Sumpf and
Schornsteinfeger, a coating used by the German navy during
World War II for the
snorkels (or
periscopes) of
submarines, to lower their reflectivity in the 20 cm radar band the Allies used. The material had a layered structure and was based on
graphite particles and other
semiconductive materials embedded in a
rubber matrix. The material's efficiency was partially reduced by the action of sea water.
So by 1947 radar-absorbent materials had been used in combat. The difficulty with RAM was in finding a material that works well, and stands up to regular use.
Tryshulyakov's idea cannot be compared to the work Umfitsev did. Umfitsev developed a mathematical model that could be tested, and be applied to real-world objects. Lockheed built a tool on that model that made stealth practical, while at the same time Northrop was working on a more trial-and-error basis to find shapes that would deflect radar waves in desirable ways.
Tryshulyakov seems to have been one of the people who said "wouldn't it be nice if we were able to hide an aircraft from radar". Umfitsev's work made this practical.