Reference or Ripoff: "Shadow Boxing" (Quote)

In this case, we're looking at a line of dialogue.

Sonic Boom's "Eggman the Video Game Part 1"

STONE FISTS

Eggman tricks Shadow, who, feeling insulted, takes revenge on Team Sonic by beating each of them to a pulp. When it was Knuckles' turn to fight, he said, "Good thing I took that shadow boxing class."

Conclusion: Reference

Sonic X's "The Cosmo Conspiracy"

STONE FISTS

Shadow wrecks havoc on the Blue Typhoon when he finds out some information about Cosmo and tries to take her out. While defending her and Tails, Knuckles says, "I've always wanted to shadow box."

I find it unlikely that the writers on Sonic Boom (a show that lives off it's Sonic related inside-jokes) would come up with a pun so similar on accident. This allusion was probably made because (cartoon-wise) Sonic X was the only time Knuckles and Shadow ever fought.

Also, Shadow beat him both times.

THE ULTIMATE

An Addition: 

I came across another case of this line in the Archie comics... 

Sonic Universe's Total Eclipse: "Part Three: Shadow Boxing"  

THE EMERALD STAYS, YOU GO!

Shadow, convinced that Eclipse (of the Dark Arms) will steal the Master Emerald, wants to move it to a secure location. Knuckles? NOBODY MESSES WITH THE MASTER EMERALD! In this case, "Shadow Boxing" is the name of the issue.

I'm assuming this was between Sonic X and Sonic Boom, so I guess Sonic Boom could be referencing this (or both). These three events are the only significant times the characters fight--maybe in Sonic Battle--I'd have to check. But given that, I doubt it's a coincidence. 

Pretty interesting how a mediocre pun can link three continuities...    

Ugh. ALSO it's a trophy for defeating Shadow in Sonic Generations. Guess it does link to the games (though that was Sonic vs Shadow).