Before the Ghostbusters arrived on the scene, Fernando (a janitor) and Jonathan had a confrontation with a ghost. Jonathan's scream apparently had scared off the flying ectoplasmic entity. He then asked the Ghostbusters to look around the place for it.
Later, in the main theater, the Ghostbusters started firing at the ghost and appeared to get a handle on the situation. Yet Jon was worried they'd damage ornate art deco designs in the room. As a piece flew through the air, he screamed once again. However, the Ghostbusters managed to catch the specter, and Jon then walked out with them.
McDonald, a comedian best known for his work on the TV show MadTV, has appeared in multiple other films with Melissa McCarthy: 2013's The Heat, 2015's Spy, and 2016's The Boss. Both of the latter two movies were additionally directed by Paul Feig (who did the 2016 Ghostbusters film).
McDonald's scene in the newer film parallels the events at the Sedgewick Hotel in the original film (in which Slimer makes his first appearance), and the character has the same sort of "snooty" appearance as that of the original film's Hotel staff.