Garden wardfare 2 chomp canceling

ok I've been playing gw2 for a week now. I like playing as the chomper. I've come across something that I can't find the answer to. I have had 2 game were I burrow in the ground and come up on a engineer zombie the stares down my chompers mouth then jumps
right out. ???? How is he canceling this out? I've spent one whole game trying to eat him but he keeps getting out. Is this a glitch or is there a button he can push fast enough or repeatedly to allow him to escape or is it just the class?

:)

 

Plants vs Zombies Garden Warfare 2 ( UNICORN CHOMPER)

Unicorn Chomper is a Special Character that can be unlock by those players who reach the maximum level (313) from the first Garden Warfare

+NOTE: You got until 2017 to get the maximum level on the first Garden Warfare to recieve Extrême pack office your hardworking.

- Check your mailbox on Garden Warfare 2 -

- You can import all the characters you've unlocked on first Garden Warfare (Xbox 360 / Xbox One) just check out your mail box once you start Garden Warfare 2.

 

Brains!!!

Electrician engineer is my fave zombie - great for gardens and graveyards, I think it's a tie for either agent pea or hot rod chomper on the plants side.

 

The engineer is immune to the chomper from below the ground if he's riding his jackhammer.