Right, so either the initial drop was completely irrational, or the last months partial recovery is completely irrational, or some combination.
I don't think this necessarily follows. The market cannot predict the outcome of future events before they happen.
One could make a rational case for the market to drop a lot on early news of COVID spreading in the USA and Europe when we didn't know how bad it was going to be. And another rational case for the market to move back up once new information came to light. Specifically:
1) The US healthcare system doesn't appear to be collapsing in the way many feared it would in the period where Italy was still experiencing exponential growth in daily deaths.
2) Congress passed a $2T stimulus package. A week before it passed I never would have guessed anything like that would ever get through McConnell's senate. But once it passed it decreased the risk of individual companies going bankrupt and increased the risk of significant future inflation.
So as I said, I could see the initial crash being rational with the information the market had at the time. And I could see an subsequent increase being rational with the two new pieces of information that later became available.
That said I never would have expected the market to be down only 10% from the peak in the situation we now find ourselves in. So I'm not arguing that it
is rational. Just that isn't
necessarily irrational.