Adding to above answers,
Yes, competition can impact click accuracy, because the click forecast is based on historical data collected by AMO and due to competition the click volume is different from ongoing trend, it reflects as click inaccuracy.
A massive budget shift can impact this accuracy too as the forecast remains based on the historic data.
In case you experience major inaccuracy for some days it is recommended to exclude these dates for Data collection bucket, such that the forecast is not impacted by these outliers.
And in case it is major budget change, the impact on accuracy will settle down as mentioned by Ritika.
Further if there are constantly changing trend in your data, it is recommended to keep a shorter Half life for the model, thus allowing it to respond to these changes more accurately.