Ryzen CPU's boosts individual cores to max clocks from idle so it's perfectly normal. AMD calls it a 'rush to idle' to get transient processing loads done as soon as possible and put the core back to a deep sleep state for energy conservation.
The thing is, Windows is never truly 'idle'. There are over 100 background processes on my system...almost 3000 threads. Most aren't doing anything but one or two are always 'waking up' to do something. That's what you are seeing.
Both how high and how long it holds the boosts depend on thermal and power margin. Your motherboard must be set up to tell the processor there's good VRM power margin, and cooling must be good enough to keep the processor fairly cool. That's why you're getting 50Mhz over the rated max boost clock.
And lastly: yes. Left on stock settings Ryzen processors effectively overclock themselves when they boost the way they do. But it's by design and it monitors itself with sensors all over the CPU. As it gets warm it will lower both clock and voltage to keep itself safe.
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