The drama doesn't appear to have been about open source. Nor CAD software. Nor anything important.
It looks like a few very old incidents which established mistrust, followed by 9+ years of petty online criticism and arguments and bickering, plus recent misunderstand of who works for SparkFun, appears to have escalated out of control.
I've learned of this situation after SparkFun sent their letter, cutting off Adafruit's ability to buy directly (they can still buy indirectly). I didn't directly observe any of the drama as it unfolded. The best info I've found about what really happened is in comments on this Hacker News headline:
https://news.ycombinator.com/item?id=46616488It has 533 comments. Many are from Adafruit. Most are uninformed opinions or off-topic conversation. None are from SparkFun, whose official statement says they aren't commenting anywhere else.
The apparently well informed 3rd party comments start about 2/3rds of the way down. Most cite social network sources, so if you don't have time to read 533 comments, visually scan for links after scrolling past the first half.
Some of those linked social network conversations have links to Github Gist pages which claim to be the emails that violated a Code Of Conduct. The offensive message may have been considered the final straw because it was sent to an uninvolved corporation's general contact address, which distributed to many other people.
All this talk of open source and CAD software is valid, but don't fool yourself into thinking that's what the drama between Adafruit and SparkFun was about.
You can find out what happened by reading SparkFun's short official statement, Adafruit's side of the story in their many comments (all lowercase messages), and the comments from people who appear to have seen this drama unfold. If you do, I believe you'll probably be in disbelief of how drama of so little substance escalated so much. I sure am.