I'm pretty sure that was me. :)

"Pure convection" is when the only heat is coming from the fan element. "Convection bake" is when the heat is coming from the bottom and the convection feature is also running. It sounds like your oven doesn't have pure convection mode.

There is no culinary difference between baking and roasting, but often electronically controlled ovens distinguish the two because the programmers have created separate algorithms which they think are better for baking vs. meats. These may or may not be accurate, but, as far as I know, the exactitudes are particular to each oven, so the best way to determine the difference would be to read up all the maker's materials, and perhaps ask the customer service, tech help, or repair service. It could involve such variables as quantity of heat balanced between sources, speed and direction of the fan(s), etc.

Agree with polllog that you have to consult with the manufacturer as many times these things are not in the user guide. The roasting mode is often more heat from the top. Convection bake may be a slower speed fan and more heat from the bottom. Miele and Gaggenau have even more complex modes.

You might be able to hear the difference between high and low speed on the fan in your oven if there is a difference between bake and roast or high and low in various modes.