Men’s brown print short sleeve collared shirt. Size XL Silk?

This shirt was given to my husband as a gift and he was told that it was silk. However, there are no tags so this cannot be confirmed. I do not think it feels like silk and is likely a synthetic fabric. It is a fun shirt anyway with a unique print in various shades of blotchy brown. It fits like an XL but please see measurements in photos to confirm your sizing. Resort wear