The presence of white smoke after adding flush oil to your Pulsar 150's engine oil could indicate a few possible issues.
Overfilling: If you added flush oil without removing an appropriate amount of existing oil, it could have caused overfilling. Overfilling can lead to increased pressure and result in oil being forced into areas where it shouldn't be, such as the combustion chamber. This can cause white smoke as the oil burns along with the fuel.
Leaking Head Gasket: A faulty or damaged head gasket can cause coolant to leak into the combustion chamber. When coolant mixes with the fuel and burns, it produces white smoke. It's possible that the flush oil revealed an existing issue with the head gasket, and the timing coincided with your oil change.
Condensation: In some cases, white smoke can be caused by condensation in the exhaust system. If the bike was left idle for a while or exposed to cold or humid conditions, moisture can accumulate in the exhaust. When the engine heats up and burns off the condensation, it can create white smoke. However, this is usually temporary and not a cause for major concern.
Given that your bike is only a year old, it's less likely that there is a serious underlying issue. If the white smoke persists or you notice any other abnormalities in your bike's performance, it's recommended to consult a qualified mechanic or take your bike to an authorized service center. They will be able to examine your bike in person and provide a more accurate diagnosis and solution.