And maybe he was climbing higher than his RFL, and maybe you (or him) had asked for a direct, got it, and you (or him) shouldn't have been there at that time regarding the flow control. So, maybe, because of you (or him), there was a traffic overflow...In the end, whose fault is it ?
Don't answer : that's the controler's responsability. Which ATCo ? The one who screwed the clearance or the one who gave the direct ?
A controller with a decent level of english could solve the thing by just saying "you've got crossing traffic 1000ft above in XXX miles, suggest you reduce your rate of climb".
By the way, next time you fly in the back of an airplane I hope you fly your FPL filed level straight through a TS or for 1 hour through turbulence with the child sitting next to you vomiting on your shoes so you will know what it feels to be out there in the hands of people like you.