Sometimes fire in forests is a good thing – to help remove ground clutter and encourage new growth. Sequoia’s rely on fire to heat and release seed cones and by clearing the ground beneath them to aid in seed germination. The trunks of sequoias are somewhat fire resistant and they can withstand minor fires without significant injury.
This tree wasn’t so lucky. My guess is it may have been struck by lightning, as the upper portion is burned out and trees (non-sequoia) around it, while stripped of their leaves, appeared to be alive and are not charred.