Well, the flu doesn't infect 100 million Americans in the same quarter. Just to mention one way in which Covid-19 is clearly worse than the flu.
50 million Americans getting the flu in any given year is pretty typical, although flu season is a couple months longer than a quarter.
Without significant mitigating precautions, which was the context for this discussion, the USA would very likely have more than 100 million Covid-19 infections in the next three months.
Yes, it's technically a logistic process rather than exponential. But there is no pre-existing immunity, so it won't hit the inflection point until it bumps up against the natural limitations. Meaning herd immunity due to a large percentage of potential victims already infected, or limitations in how many people will likely meet a sick person. The latter won't happen without the mitigations I'm talking about.
A third of the population infected seems as reasonable a ball-park guess as any for when the first point would be hit. But I really, really hope that the mitigations prevent this.