When uploading a sketch to an esp8266, isn't that the same as "flashing firmware"? I thought that I read that using a PC running the Arduino IDE to "upload a sketch" to an esp8266 overwrites the original firmware (with the AT commands), and is actually "flashing the firmware" each time a "sketch" is uploaded. If I have that right, then why does the esp8266 WiFi still visible in available connections? There must be some code instructing the esp8266 to do this, but where is it? My sketch was simply the hello blinky thing and contained no #include statements. Where have I slipped?
Uploading a "sketch" is indeed "flashing firmware".


  why does the esp8266 WiFi still visible in available connections?


I'm not sure what you mean by that.