Indeedee's SV OU "Choice Scarf" sample set includes Mystical Fire, a move it cannot learn in generation 9. The move database is correct — Mystical Fie is not included in Indeedee's "Moves" list — it's just the set that contains an illegal move. It's just a sample set, yes, but probably good to correct nonetheless — indeed, this discrepancy confused a user in the Showdown OU room.
(Apologies if this should go in the Bug Reports thread instead; I assumed it fits here as it's not a database error, just a set error.)