First let me say that to answer your question is impossible because we can;t tell what other changes you may have made to your over all preparation. However I can speak in general about this topic.
I have had pretty extensive experience with using Hypoxic tents to prepare athletes for sea level competition. The mechanism there is well understood and there is good evidence that the hematocrit increases with their use and a decent correlation to improved sea level performance exists. Same things can be said for sleep high/train (or race) low techniques which in many cases to improve performance. But the results of the many studies and anecdotal evidence is not still not 100% conclusive. With IHT there is even thiner evidential support. The main test the article refers to was sponsored by the company making the device. Hypoxico does the same with their IHT devices. Already a rather dubious practice that should give you pause.
As the author says. He sorta, somewhat, maybe, thinks that, maybe this device did something but he can’t really tell. At least he is being honest but that is not exactly a glowing recommendation. So, why are you surprised that it was not magic for you?
Understand that any study done in a lab to discover the efficacy of some training intervention has some serious limitations that make the study’s results less than 100% predictive when applied to the real world. I’m not familiar with the study quoted but here some of the common problems with trying to make conclusions based on lab studies.
1) The duration of the test. Usually short.
2) The subjects. Usually untrained college students looking for some easy money.
3) The study looks at some physiological parameter rather than performance. maxVO2 is a favorite.
4) The study looks at mean changes of the groups in the test parameter with standard deviations.
The problems that often arise are that untrained, or less well trained individuals will respond readily to almost any imposed training regime, especially ones designed to improve maxVO2 which is known as a first wave response. This means that maxVO2 responds very quickly among the young and poorly trained but is almost unchangeable among the athletically mature.
The conclusion of this study was that there was an increase in maxVO2 that ‘could’ (maybe?? my emphasis) result in tiny improvement in a cycling time trial. MaxVO2 does not correlate well to endurance performance among well trained athletes (r2=.6 many studies) where as economy and speed at the lactate threshold correlate much better (r2 form .8 to.95). So, it seems this study largely hinges on the assumption that improving maxVO2 will make you faster. For some folks it will for others it won’t. On top of that, the standard deviation in the results of this sort of test tend to run in +/- 10 to 15% range. This means that while the average improvement of maxVO2 (not performance, remember) is say 2% and there were some who saw much bigger improvements, there are an equal number that actually saw a significant reduction in the parameter being tested (maxVO2).
In short it is no big surprise to me that you saw a decrease in performance. I suspect your early pacing error had more to do with this than using the device or not using it did.
There is not good evidence that this device improves your altitude performance or acclimatization. The performance we see in our athletes be they runners or climbers or skiers is 90% the result of their training and only a tiny increment can be gained with most magic like diet, supplements, Hypoxic sleeping or IHT.
I hope this helps,