This is another example of what I alluded to on the "Wyndham" thread. Looking at Walther on ebay yesterday there is also a Sowerby set no. 2638 being sold as Walther. Sellers seem to be loath to do any research themselves, all to often relying on another example on the site and accepting whatever that listing says without question.
As to why this Boom set is named "Gorlitz", not so long ago another piece named as "Gorlitz" caught my eye on ebay (possibly a lidded trinket bowl?). I thought at the time "That doesn't look like Walther at all" and passed it by. Possibly whatever that was (it's now dropped off the "Completed" listings page so I can't find it), it possibly looked like this mis-named blue set.
Sadly, there seems to be much more copying and hence more mis-named pieces on ebay. To be safe I disregard many of the ascriptions on ebay and etsy unless I either know them to be correct or can verify them elsewhere. These days IMO almost everything that is written about glass on these sites is best taken with a pinch of salt, so much is pure guess-work.