My brief research suggests you are correct about the difference between designation and approval. The approval is the final FDA approval that will come after the appropriate PH-I,II,III testing etc.
The most direct benefits of orphan drug DESIGNATION I could find were reduced costs and perhaps greater emphasis on timely reviews by the FDA:
"Orphan designation qualifies the sponsor of the drug for various development incentives of the ODA (Orphan Drug Act), including tax credits for qualified clinical testing. A marketing application for a prescription drug product that has received orphan designation is not subject to a prescription drug user fee unless the application includes an indication for other than the rare disease or condition for which the drug was designated." https://www.fda.gov/ForIndustry/DevelopingProductsforRareDiseasesConditions/HowtoapplyforOrphanProductDesignation/default.htm
Perhaps investors found the orphan drug DESIGNATION and thought it meant the same thing as approval; I hope there's more behind the price action than that!
My greatest concern with the significant weight this stock has in my account is that lately when great news does come out, they almost immediately take advantage of the rising stock price to announce more dilution. I'm tempted to sell into any price jump as fast as I can to beat their dilution lol.