condensation of tellurium on inside of ampoule?
This is a general phenomenon. All substances at any temperature above $0\ K$ will shed a few atoms from the solid or liquid, forming a gas however dilute. The tendency for this to happen varies with temperature, and it can be measured by determining the equilibrium pressure of a substance inside an evacuated chamber. The key concept behind this is vapour pressure. There are several previous Chem.SE questions regarding vapour pressure, so you may find something useful, such as perhaps this.

As a rule of thumb, the higher the boiling/sublimation point of a substance, the lower its vapour pressure at any given temperature (in fact, the definition of the boiling/sublimation point is the temperature where the vapour pressure equals the pressure exerted by the surroundings onto the solid/liquid substance, which is in many cases equal to $1\ bar$). Tellurium is a relatively low boiling-point solid, with a vapour pressure of $1\ bar$ at $988\ °C$. According to this article, the vapour pressure of tellurium at its melting point ($450\ °C = 723\ K$) is approximately $70\ Pa$. This means there is a fair amount of tellurium vapour present inside the ampoule at this temperature. It is entirely conceivable that some of this vapour could deposit in small droplets on the upper surface of the glass ampoule, outside the main body of the liquid. Note that theoretically the deposition of tellurium on the upper surface should also happen at room temperature, though the equilibrium vapour pressure of tellurium at $25 °C$ is only about $5 \times 10^{-4} Pa$, which would make the transfer of a macroscopically visible amount of tellurium an extremely slow process.