You sure about that? I don't think that was the case.
I mean, look: Mii Swordfighter had a freeze glitch, and there were shield clank files similar to the ones you'd hear on the Links, and we eventually got Hero.
Same with Duck Hunt minus the shield clanks, and we got Banjo then.
I don't remember if there was anything found for Terry.
Simon/Richter had a whip glitch for his Side Smash, and since Byleth had a whip sword in their set, it's pretty safe to assume it'd be them.
And finally, Bayonetta had a texture glitch when she uses Side Smash, and what do you know, Min Min got announced just yesterday, and like Bayonetta, she has something related to changing textures!
I don't see how anyone would attribute those to faulty SD cards, but so far, "glitches = new fighter hint" isn't letting up yet.