The boiling point of lead is 1749°C. You're not going to get lead vapor from the solder at the temperatures of a toaster oven. The smoke is probably from some plastic component or some remaining flux on the board. But yeah, that oven shouldn't be used for food anymore.
Liquid lead has a certain amount of vapor pressure even before it boils. Just like you can have water evaporate even when you're at temperatures below 100 C you can have lead enter the air even when you're below 1749 C.
There is no leaded solder any more in consumer electronics. Even for leaded solder, the smoke comes from the flux core. You'll notice melting unfluxed leaded solder produces essentially no smoke.
Solids also have a vapor pressure. Yes you've increased the vapor pressure, but you're way below the temperature where significant vapors are released.
