The 19-year-old striker was one of four new faces named in Billy Stark's 18-man squad for next Wednesday's match against Greece in Corinth, with the Scottish Football Association using its own Twitter account to break the news.
And ahead of Saturday's William Hill Scottish Cup fifth-round tie against Inverness at Rugby Park, McKenzie, who represented Scotland at Under-19 level, told how he was one of the last to know about his step up.
"I'm not on Twitter so all the boys knew before me," he said. "I'd just come in from training and the boys told me.
"I'm about the only one who isn't on Twitter. I can't be bothered with it, I'm on Facebook but Twitter, it's too much for me.
"It was a bit of a surprise, because I wasn't involved in the last few camps, which I was a bit disappointed about. I've been playing the last couple of weeks in the first team, so it's very pleasing."
McKenzie scored in his first start for Killie in the 3-1 win against Dundee United at Tannadice in August and is glad that boss Kenny Shiels is giving youth a chance at the Ayrshire club.
"It was a good start to the season for me with getting the goal against Dundee United," he said. "I was playing a lot but it has been quite a bit stop-start since then.
"I started against Dundee last week but was disappointed to be left out against Celtic in midweek, but hopefully I start again (against Inverness).
"The manager is not scared to throw young players in which is great. We've got a good youth team and it's good knowing that you will get a chance. We were knocked out early on (in the Scottish Communities League Cup) at Stenhousemuir so we've got a point to prove."