There was a time when people thought a ball of fire moving across the sky every day must be alive. The universe is full of strange phenomena perfectly explainable by physics. This is no different.
It's really not "perfectly" explainable by physics since we don't understand all aspects of physics yet. If you said "mostly" explainable by physics I would believe you.
Also, if an alien happens to be shining a beam at us rhythmically, that's also "explained" by physics but we won't actually know if the source is a natural phenomena or an alien shining his super flashlight at us.
Of course life at a deep level is just physics. But given that the information content of this signal is relatively low (regular patterns of repeats) and that the amount of energy it requires is immense, I'd bet much more heavily on a natural phenomenon than life-directed activity.
I’m not saying there’s evidence, I’m just pointing out that it’s a strange dichotomy to say that one one hand, we have explainable phenomena, and on the other hand we have extraterrestrial life. If we ever do find proof of it, I don’t understand why the assumption should be that it won’t be explainable.
The problem is, any form of intelligent life that exists in the same universe as us is going to have to be able to be explained by physics, since that’s what physics does - explain the way the universe gives rise to the phenomena in it which we observe. I mean, if we detected signs of intelligent life that can’t be explained by physics, that either means we have some new physics to discover, or physics has to give up because it turns out there is a form of life not subject to its rules.
"Greetings from ___." "Oh, hello... uhh, so those signals were your house and not a trefoil of two black holes and a quasar?