Hi,
I hate to burst this bubble, but to state that we can get a sine wave out of a 555 is not really true even though we see what looks like a sine wave on the 'scope'. That's because it is not coming directly out of a the 555, it's coming out of the LC network. There is never a doubt that we can get a sine wave out of an LC network with the right values chosen, but there's still no way it is coming from the 555 itself.
Just to note, almost any wave shape that is fed into a filter like a bandpass filter will produce a sine wave. That includes a square wave, triangle wave, rectangular pulse, etc.
There also appear to be what looks like a redundant resistor in there.