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This panel is saying a few things;
• Tobirama has seen a Kagutsuchi before.
• Somebody in his generation used both Amaterasu and Kagutsuchi.
• They kinda sucked at using Kagutsuchi lol
Madara and Izuna were the only known Mangekyou Sharingan users during Tobirama's generation. So its safe to assume Izuna or Madara used either of these techniques