If you look closely at the card, you will notice that Sawchuk is wearing a golf shirt under his uniform.
In Ken Reid's book "Hockey Card Stories", he was able to track down the players to ask about their hockey cards. Sawchuk passed away in 1970, which allows us only to speculate why he might have been wearing the golf shirt under his uniform.
During the early years of cards, photographers would show up without notice to take the players photos. It is highly likely that Sawchuk was called in, most likely on the road due to the away jersey in the picture and placed his uniform and equipment over his street clothes.
We will unfortunately never know the story behind the golf shirt as it died with Sawchuk in 1970. I'm sure it was quite the story.