These discoveries reveal that the simplest living cell is so intricate and complex in its design that even the possibility of this coming into existence accidentally is unthinkable.
Unthinkable? Maybe to you.
What the author is saying is that if they can't figure it out, then no one can. That's a pretty bold statement, don't you think? Are they the world expert on everything? Nope.
The fact that you don't understand something does not give you permission to conclude that it is false. This irrational flatulence is common, and often called "argument from ignorance".