Does anybody know if there is something true behind that or is it just a hoax?
ETC doesn't require a fork to be secure. Both chains are subject to the replay error in the forks code. If the ETH community and ETC community actually care about their members they will guide all the noob members towards utilizing a split contract. Once completed; although, replay still occurs (by design of the forked code supplied by the ETH foundation) it's affects no longer matter.
You would be correct in suggesting ETC is slightly less secure due to a lower hashrate. That is only if unethical miners wanted to attack it. That is increasingly unlikely since the hashrate has grown substantially. It's unlikely that the required number of unethical miners exist. The whole concept really makes ETH supporters look bad and should be completely dismissed.
Frankly the lack of support by more experienced members of the ETH community in explaining the requirement of using a split contract is disappointing. They are potentially costing their members millions of dollars in lost profit.