Dear lord. Why does this guy have the power to make decisions??
Yes, we breathe out CO2.
Yes, while exercising we breathe out more CO2.
No, that isn’t (necessarily) bad for the environment.
That CO2 is already part of the existing CO2 cycle.
As I understand it, the thing that is (apparently) bad for the environment is introducing NEW CO2 to the CO2 cycle – which we do by burning fossil fuels (e.g. releasing CO2 that was previously safely sequestered underground).
You can’t in all honesty declare cycling completely “environmentally friendly”, because you can’t in all honesty call ANYTHING humans do “environmentally friendly”!
But what you can say is that using a bicycle for transport, instead of a car, is MORE “environmentally friendly”.