Does it do this often? If it was a one time thing can you recall what site you were on or previously browsing? Typically the GPU is still used to render your desktop actions as well as video decoding when watching youtube videos, netflix, etc.
However on a rare chance it is possible you were on a malicious site that was using your browser as a means to reach your GPU and mine crypto. Though this is a RARE chance and would have been detected by your anti-virus. Do a quick virus scan to check everything is fine.
Also if it does happen often, keep task manager open and try to take notice which chrome tab is causing such high usage.