LG has recently filed for a trademark on the X5 moninker with the Korean intellectual property rights authority. It's not just the name that's being registered, there's also a logo, with a notched X and a smaller 5 to go with it. LG's X-series currently has the X cam and the X screen models, the two positioned somewhere in the midrange. Meanwhile, the LG G5 SE exists, but it's an alternative to the proper G5 for certain markets, and not really a model to be sold parallel to the G5. It would make sense then for the LG X5 to be a more affordable version of the G5, inbetween the the...
Source: http://www.gsmarena.com/lg_trademarks_the_x5_moniker_cheaper_g5_maybe-news-18378.php