No, it just disconnected the battery from the rest of the system for a short moment, making it fully reset.
Entering flash mode is an simple as holding Vol+ button while the phone is being turned on. There will be no visible indication of entering it at all (no LED, no vibration etc.) - the CPU will just silently wake up and stay on. At this point, the phone should be visible in lsusb when you connect it to a PC via USB.
Since no visible feedback can make it somewhat confusing when things go wrong, here’s a more complex procedure meant to mitigate any possible edge cases that could go in the way: Reflashing the Phone
The phone should also show up in lsusb (although with a different entry) when it’s fully booted up. If it doesn’t show up no matter what, there may be some hardware issue.