("Roger that" seems to come from American TV, I'm continuously trying to stop trainees using it.)
Strange to get two pilots responding, both appearing to be non standard.
I would not judge by phraseo. It si more than normal that on home ATC frequency you are more than relaxed, and you will not repeat frequency you repeated probably hundred times before. You can check on liveATC.net how pilots on home country frequencies almost never do readback correctly, when handed over to new control. Even if this is was handover to Vietnam control, I would not see this strange or suspicious.
And I would say, that if you know how to disable ACARS, you would probably know these ~50 ICAO phrases well enough. As you can get them
freely, unlike of T7 detailed system descriptions.