The reason for the growth over different time frames can differ. Anecdotal, but most of the IT people I know from Poland worked for, as they call it, "big corpo" and generally it's offshoring either directly with companies such as DXC/Luxoft or n-ix, or through local offices (Akamai for example). If you look at the average salary in Poland (in general), and the average tech salary + the number of tech workers there, it's easy to say a large part of the GDP is tech.
Whether or not it's offshoring is a little less obvious, but I can't think of more than 2 or 3 successful Polish tech companies.
What is the average salary, the average tech worker salary, and the number of tech and other workers in Poland?
There are other countries in the world or even in the EU where salaries are lower than in Poland. Why don't they see the similar growth? I guess this is more nuanced than just lowered salaries can explain it. Surely, that's part of the equation but to develop highly innovative economy, one needs to start with something. That's how China started, how Korea started etc.