Why crystal capacitors have to be close to each other?
Yes, there is a strong RF current flowing through the capacitors of a crystal oscillator. In order to keep this current from coupling to/from free space (EMI considerations), it is necessary to keep the loop area of this circuit as small as possible.

In this case, the "loop" is the complete path through the crystal and the two capacitors. If you don't keep these components as close together as possible, the loop area will be larger than it needs to be.