User blog comment:FairyRaven/Fairy Tail Chapter 428: When We Take Different Paths, Review and Commentary/@comment-25395791-20150413123301/@comment-7418318-20150413191710

I don't think Frosch's death is much of an argument.

For one thing it happened in another timeline, so it's possible that in this timeline he wouldn't have killed Frosch.

And for another - and this is my main reason - we don't know the circumstance. "killed" isn't the same as intentionally murdering. For all we know in the other timeline Gray killed Frosch by accident with a stray-shot or AoE attack meant for Rogue or Minerva. Or during the fight the building might have collapsed and crushed Frosch. We just don't know.