Sadly, Met-Rx is not the same company it was twenty years ago. Their quality has fluctuated from the moment Connelly & co. sold the original business they had birthed and nurtured to become one of the legitimately best quality companies in the industry.
Most recently, I understand that the brand has come into ownership of the parent company of Vitamin World.
Anyway, with the varying (sometimes poor) quality control, it may be possible that a bit of moisture got into the container during the packaging process. The container may not have been properly sealed, or there's a chance the seal may have been damaged during shipment - especially if the mailing box was damaged any.
It seems like a negligible amont of moisture, and I doubt there's anything "wrong" with the product. I routinely encounter clumping of certain powdered supplements during use. Just give the canister a shake to break it up. I wouldn't wait too long to use it, though; just my opinion. Typically, powders hold up to storage better than liquids.