Crawling before sitting??

Jasmine

My son will the 7 month on the 10th, he has zero interest in sitting up. When put in a sitting position he balances well for a few minutes before just plopping over and giggling but while on tummy he gets into crawling position with no problem and rocms back and forth/turns around to grab things. I have a feeling he will be crawling soon but is it unusual for baby to crawl before sitting independently.