The difference is that flat earthers reject objective evidence. This is someone disagreeing over projections about the future. And, to be frank, nobody has a fucking clue how to estimate the medium term effects of this.
If nobody has a fucking clue then anyone who is certain that the economy will recover in 2 months is either deluded or bullshitting themselves.
But we do know certainly that we will only be hitting the peak of infections sometime in April in states that were much more proactive than the median. It is extremely unlike that things will clear up, say, by Easter. Those who are so optimistic are innumerate and don't understand exponential functions.
Yes, certainty in future economic projections is delusional, but it’s a delusion that is well received by society. Humans prefer confidence over competence, and abhor uncertainty. Right now, we have a lot of uncertainty.