No, it has no merit. The CO2 emitted by a cyclist (or by any animal) is a byproduct of metabolizing the food that was eaten and the carbon in that food ultimately came from plant matter (either directly or through intermediate animal food sources). The plants in turn obtained the carbon by taking CO2 out of the atmosphere very recently. So the net effect on the atmospheric concentration of CO2 is zero - it's a closed recirculating system.

The difference in the case of vehicles that consume fossil-fuel hydrocarbons is that they are rapidly returning CO2 to the atmosphere that was originally taken out of it many millions of years ago. In that situation the current CO2 content of the atmosphere is being increased.