No it's not. Empty blocks can mean headfirst mining. It's since been discovered ASICBoost can be done without empty blocks or reordering transactions (though it can be done that way too) by malleating a transaction that pays themselves. This is fully undetectable on the blockchain. The only indication is that blocks will contain txes that were never broadcast on the network prior to the block being found, which antpool does.
The smoking gun is that the firmware that was extracted contains ASICBoost hooks:
http://diyhpl.us/~bryan/irc/bitcoin/bitmain-firmware/
That the stratum server contains code to support ASICBoost and the post above shows how to prove that. Open cmd, telnet into antpools stratum server and check yourself.
That bmminer contains code to enable ASICBoost.
And that people ARE using it right now. They're not wild accusations, I mean there are step-by-step tutorials explaining how to enable it and how to check antpools server supports it. Buy an antminer and turn it on yourself.
We don't have proof if BITMAIN used it, but we know for sure miners on antpool are using it right now this second.