"We can detect things we were not evolved to detect" is a non-sequitur, a true statement that does not refute the original argument. Because we can detect some things we were not evolved to perceive, does not mean we can therefore perceive aliens.

I mean no condescension when I say that I know that is a difficult concept to grasp. Everything we are is perception, pattern recognition, threat assessment, problem solving. That there might be something important in our environment that we are simply not built to respond to is far easier to reject outright than to consider. In fact, it is literally meaningless speculation. This is why it's my favorite, because it is so challenging to consider.