it is correct that the ubuntu company cannot prohibit people from copying and modifying stephane's code, or indeed the entire previous version of lxd, under the terms of the apache license. but they can certainly keep using his code in new versions of lxd under agpl
in fact, apple can use stephane's code in a proprietary lxd derivative if they want to. that's what the apache license is designed to permit
if you want to prevent people from using your code in a more-restrictively-licensed fashion, don't use the apache or other bsd-like licenses; use a copyleft license like the agpl. and don't sign a cla