Phones are like computers and like computers, like they act up and do things they aren't normally supposed to do. This is probably one of those times. Turning off and turning your phone back on will 'refresh' it's system (like when you restart a computer) and can potentially fix these issues.
Networks are an odd thing sometimes, perhaps as two messages got sent to you at the same time and the network had a little hiccup and mistook the sender of the message. As Ahmad said, restart your phone will help, it happens nothing much to do about it except restart your phone or just the messaging app you are using