Is this a glitch or...

Well I was just playing some Lockdown, and this person on the other team (I won't give his name) kept walking the whole time like he had been stunned, yet he hadn't, and whenever I attacked him it never did damage. Afterwards I asked if he was hacking, because well it seemed like it, he said "no" and the conversation led into what Mod he'd been using, he said Guardian but when I saw him he had been using Recon.
So, is this a glitch, hack, or something else...?
it actually may be just lag, was he walking through things?

He wasn't walking through things, and I know people lie about hacking, and I had 4 bars of connection when I checked.

yeah my last suggestion he learned a trick to infinate cloak himself

he was a guardian. your client didn't draw his armor and shield so that it looks like he's walking when he's actually blocking.
some people lie bout hacking to avoid being reported or did you check ya connection if it was 1 bar you'd be glitching alot and not takin damage if not maybe some trick he taught himself to have aload of cloaking