What means 'swing'?
A swing describes a zig zag movement of the price. Cryptocurrencies are generally considered to be very volatile assets. In the past huge price swings within relatively short timeframes were observable. During the crash in 2018 Bitcoin has lost over 2/3 of its all-time high value within a period of a few months.
why do 'swings' occur?
In the 21st century is characterized as the century of information. News and tickers are available for everyone, everywhere at every time. In markets this results in unpredictable price movements due to the masses of information created everyday. Especially unregulated and small markets, like cryptocurrencies are highly sensitive to negative or positive publications of the mass media. The high accessibility of information in combination with the relatively small market size make cryptocurrencies affected by huge price swings.