Google says

> RuBee is an acronym for "Radio U.S. Bureau of Engraving and Printing",

Weirdly not related at all to Zigbee's naming origins, in spite of their technological similarity.

RuBep? As ever, the fastest way to get a correct answer on the internet is to post an incorrect one:

> The Institute of Electrical & Electronics Engineers Inc., the international governing group for such technology, has designated P1901.1 as the technical designation given to the RuBee technology, which was named RuBee by Visible Assets. "There is no real reason we named it RuBee," said Mr. Stevens. "It actually was named after the song 'Ruby Tuesday.' It just sounded good."

https://theproducenews.com/print/pdf/node/1355 (PDF)

I'd assume "ZigBee" was also an inspiration.