Yes. The Pi3 could always boot from USB once you enable[1] it. The difference with the Pi4 is that it's initial boot eeprom is now updatable. The first release didn't include the option for USB booting. It has just recently been added [2].
The other major difference is the Pi 4 has USB 3.0 and the network interface is not on the same bus. So, while the 3/3+ also benefit from USB boot, the 4 can benefit quite a bit further!
Earlier Pis could already run off USB drives, it’s just that they released the Pi4 before they had USB boot in the firmware so it didn’t work, but now it does.