I'm not quite sure about the exact bidding sequence but that was surely the contract (and the declarer). The thing is that the ♠10 was led, East asked about leading agreements and North responded they led 3rd and 5th. East put up the ♠J and ended up down one.
I guess there should be no redress as east goes down no matter what he plays to the first trick. It is even naive to think they'd lead the 10 from AQTx (but it could be AQT9(x)?). The thing is that I'd like to know what should the proper answer be to the question: How do you lead? and whether the asker or the answerer should pursue the matter further in a case like this. Or for example, someone leads the Ace and the question is made, can the answer be: '3rd and 5th'?
Thanks for clearing this up for me.