I'll let Tim select Andrew's answer as best, but he hit the proverbial nail right in the nucleus.
FTDNA has added just under 2,000 new branches to the yDNA haplotree in only the past 60 days. There's no real-time application interface that allows WikiTree to check those data, but I do believe that Aleš periodically downloads the JSON file (a text-only form of database information) that FTDNA makes available and uses that to compare against entered yDNA haplogroups.
I confirmed that E-BY5244 is absolutely a branch in the haplotree, so I'm sure that it was added recently, sometime since the last manual download of the FTDNA JSON file. So you can either just leave the suggestion as it is and wait until the next update of the haplotree data, or mark it as false and continue on.
