Stealing a spell from opponents graveyard is filled with mana and other problems.

In my recent match I encountered something puzzling.

I played AIX with Angarth against Bolas1.

In my turn 7 I played “Dire fleet daredevil”. I’m pretty sure that my hand was empty, yet I stole a BSZ (blue card in a red/black deck, so definitely not my card) from my opponents Graveyard. BSZ got 6 mana according to DFDD, then BSZ was cast with full mana i.e. 16 mana. Is there a card that will do this or is this due to my opponent had cast this card with full mana?

is that correct behaviour?

This was quite confusing, but it got even weirder, because then the log shows “Exploring the Wilderness - player” was cast a second time this turn, which is only cast a the beginning of a turn.

That must be a mistake.

Finally, a little later a noticed that the first card in my opponents hand was marked as a card which had full stored mana even though the opponent cast several cards that did not use stored mana.

This must also be a mistake.