No, this is not an April Fool—Essential is still updating the Essential Phone with remarkable speed. The phone, which launched in 2017, is getting its April OTA update at the same time as Google's phones. There are some minor tweaks to functionality, but this is mostly about security patches.
Early on, Essential made a habit of launching OTA updates at the same time as Google. This phone got Pie on the same day as Pixels. The OTA includes the latest April 2019 patches, just like the Pixel phones. Plus, there are some adjustments to minimum brightness and volume settings. The OTA clocks in at 74.3MB.
If you've got an Essential Phone, you can probably get the OTA immediately if you head into the system settings. Essential probably hasn't moved enough phones to bother with staged rollouts.