It's a cumulated graph. Earlier flu seasons were responsible for excess deaths in 2018 and 2019, and since flu season starts earlier in the year than pandemic deaths, by April, more people had time to die than has died in total from covid-19 in 2020 so far.

You can click the "weekly" button and you'll see that covid-19 is deadlier than earlier flus, but has been killing people for a shorter amount of time.