User blog comment:B214/Question & Answers 5/@comment-82.199.195.143-20151012163215/@comment-120.161.1.90-20151012165141

Three possible explanations

1. Small amount of his demonic power were still restored in his Boosted Gear, it was first shown in vol 6 as i recall.

2. His new body has something to do with it ( Great Red's body is not your usual dragon's body you know)

3. Ishibumi was just being careless.