Why do they say a Turing machine is a imaginary concept (which is correct), then say ENIAC became the first one, but then maybe not?

Thanks for pointing out this hilarious section. A Turing machine is an “imaginary concept” just like any of mathematics. An abacus is also an “imaginary concept”. But people can still make them (at least finite versions).

When they start talking about “imaginary concepts”, it’s pretty clear that the author has no understanding about the relationship between math, science, engineering, etc. That lack of understanding is a necessary prerequisite for writing this kind of article.