"Boom!!"
A huge was created and almost you can see the training ring got crushed. But fortunately it wasn't as weak as you think. It is already able to handle that attack but at the same time Allen already jumps backward.
As you guess, Allen was fighting. He wasn't fighting with any student but he was fighting with his teacher and this time Fiona also took this fight very seriously. Even though she wasn't even using the 10% of her strength, still as you can see the power behind those attacks.
On the other hand, naturally Allen uses his full power (not his bloodline power) to fight his teacher and at the same time he also reveals to her teacher that recently he got a new technique called flame bullet. Well he decided to reveal that he got that technique from his old teacher. Naturally Fiona was surprised after seeing that technique because that was powerful and by observing the power she could also tell most likely that was a high grade technique.