A similar thing happened to me last month. I was at home in the US but according to SPG I was at a Starwood hotel in Europe where I had evidently used my Starwood number.

Rather than sit back and accept the points for the stay (one option I guess) I called the SPG PLT desk and asked them to check it out for me.

The SPG PLT person called me back and said that another customer had checked in with an SPG number similar to mine. The front desk had entered the number manually and I guess not noticed the different name.