The key to this sort of trademark claim is likelihood of confusion or perhaps implied endorsement in having a common-sounding name. Where it is obvious that two companies are in entirely unrelated fields, then the holder of the mark who wants to shut others down had better have a very strong mark such that any use by others of something that sounds similar implies affiliation or endorsement.
There is no way that this is the case with the "zen" prefix.
Even on a personal level, I represented companies known as Zentek Strategy and Zentek Technology, the latter of which became a $2B market cap company before having issues in 2008. We filed and got a registered trademark for "Zentek" and held this from about 1990 through 2008 when the company had some problems and shut its operations. The mark that we registered was not even in Class 9 (where most tech companies file for marks) but in another class because there was already another long-established "zentek" company that held a registered mark in Class 9.
So, wow, the claimant here says, in effect, "we have been using 'zen' since 2007 and so we have a right to claim this exclusively as our own." And it then proceeds to file formal proceedings against all sort of other companies to force them to spend large sums of money or else give up using their marks that share only a common prefix.
Call it what you will. I call this abuse, pure and simple. I can only hope that the people doing this take pride in their coolness as zen proponents even as display the height of arrogance in how they choose to act.