This is a trait of a modified Pokemon; it's a hack.
This is an example of the invalid relearn move flag that showed up for an event Diancie (the shiny Japanese one), and this error comes up for all 4 of its moves. The traits of it are:
TID: ポケセン
SID: 00131
OT: 12125
Name: ディアンシー
Moves: Return, Reflect, Moonblast, Diamond Storm
Other: Timid nature, level 50, Cherish Ball, origin from Omega Ruby, received on 13/12/2015 (the PowerSaves date is 12/12/2015 according to
this Reddit post).
Country: Japan (Tokyo)
I'm not sure what else is required to work out this error. The same Diancie also gives the warning:
Is this saying that the friendship of the Pokemon has been artificially changed?
I'm getting this error for evolved forms, specifically Milotic with Splash and Zoroark with Fake Tears. I would say that this is a false flag from PKHex, but the same Pokemon also give this error...
These pokes were 'caught' on
Route 19 in White 2. It's pretty clear that these guys are hacks, but I was just wondering if the Invalid Move error is a cause for concern for Pokemon who can learn the said move in their previous evolutions, but not the latter? One example I can think of is Chimchar and Flamethrower (I was quite annoyed to find out that Infernape couldn't learn it in Diamond and I had to use a precious Flamethrower TM to teach it to him).
Finally, I'm guessing this is just a badly genned 'mon (genner forgot to put Egg Moves in the Relearn section).