"better altitude hold by software" indicating that they are not
using standard ArduPilot firmware, but I believe the GPL
software license under which ArduPilot is distributed mandates
that if you copy-and-modify the software, you must also release
your new software to the public. The spirit is that since you
got it for free from others, so you need to keep it free for
others to use/modify too.
Sorry, common misconception.
The act of copying and pasting the code into their own code doesn’t mean
they must release their source code to the public. It does become covered
under the GPL, however, and is constrained by the GPL in various ways.
One of the critical things being covered by the GPL means is that if they
distribute a binary produced from that source code they must also notify
that user of the availability of the source code and produce that source
code on demand, licensed under the GPL.
This isn’t to say they company in question hsa done this - I’ve no idea.
But it takes a customer who cares enough to find out.