This sounds like total balls to me.
I'm no conspiracy factualist but how come every large "terror" event in either the US or UK in the last ten years has been either during or right after a "drill", or the security services "knew" about the perpetrators beforehand? Don't believe that? Check the facts. 9/11; 7/7; Boston; Sandy Hook etc etc. All had "drills" running concurrently with the event. Lee Rigby's attackers were "known" to both MI6 and MI5. A mate of the perps went public right afterwards saying he had also been approached to be "recruited" by SIS. He was arrested straight away for "terror offences". Funny that.
A suspicious person might think they had picked up the wrong bag in another "drill". Also funny the threat level was raised right afterwards. Another suspicious person might speculate the two were supposed to be connected. Not me, obviously.
Also, when did airports start handing out replacement suitcases?