I don't use the web installer, but from what I understand, the process in webUSB would be similar to flashing in the console. I forgot if the screen is supposed to blank, but its possible when the vendor partition was flashed your device committed some kind of restart (either flushing the titan chip keys or flashing the new boot signature key into the device)
Regardless, if it flashed, turned on, and functions normally, shouldn't be an issue.
It may of also just restarted and thats just apart of the process of flashing