Did the prompt and x undergo Concatenation or Addition?

[sunday6666]

The code in Polarization Prompt Fusion Block (PPFB) is
qkv = self.relu(self.qkv(torch.concat([prompt, x], dim=1).reshape(B, 2C, HW).permute(0, 2, 1)))
This means that the prompt and x have been concatenated, but in the paper, it's addition. Which one is correct?