surge protector strip

i live in 2 story house. 2nd floor rarely used. I have central air conditioner, heater and hot water tank on second floor. I had surge protector strip plugged in wall. i was downstairs and air conditioner was not cooling 1st floor well. I heard explosion upstairs. I went upstairs but did not smell any smoke so i dont know where explosion came from. i could not turn lights on in room where air conditioner is. All fuses looked normal. I called electrician next day and was told surge protector caused explosion. He fixed fuses and i got lights back in air conditioner room. surge protector did not have any signs of being burned. so my question is is it really possible? Is electrician telling me the truth? How is small surge protector that was just plugged in in wall and nothing was plugged or used in surge protector cause explosion? And if this possible is it indication of electrical supply in general? i have 20 year old home and run computers, tvs, air conditioner, etc. Nothing unusual. But home was not build well.