I quite often left Kings Cross Thameslink and walked West to Euston. This meant I walked across the front of Kings Cross mainline station. Usually I was on the opposite side of the road. When I returned, I was on the same side as Kings Cross mainline station. There would always be people hanging around. I was walking with a purpose and they never bothered me, but I imagine that drug addicts would give off certain signals, hang around and make eye contact with people they thought were dealers. The dealers would do the same.
Young people, possibly homeless, living in squats etc hung around. At some stage, a sort of portacabin was installed as a mini police station. It had one way mirror windows and cctv. Dodgy people still hung around though. As far as most people going about their business were concerned, the area would just seem a bit rough. But a young person hanging around might give off different signals. Someone might "befriend" him.
In the early 1980s Argyle Square, opposite the station, with cheap hotels, was a busy red light district, busy even in daylight. That was cleaned up, partly with traffic measures to stop kerb crawling.
There used to be touts for illegal minicabs approaching people leaving the platforms in the mainline station. Now there are problems with people stealing luggage. (A number of Algerians have been arrested for this.) Jenson Button had luggage, containing valuable items, stolen just outside St. Pancas (which, of course, is next to Kings Cross).
Since Thameslink trains started using St.Pancras, I haven't had to cross Kings Cross station. The whole area is supposed to be being developed. My point is that, historically, the area has always been rough. Around the world, many big railway stations attract "rough" and homeless people. beggars and sex workers. (I recently witnessed this around Geneva railway station.) I suspect that the area behind the station is still somewhat rough.
Most people get off trains and enter the tube system within the station or get taxis from the rank. Some old hands get the bus. When I was young, living in Lincolnshire, and used the Kings Cross mainline station, my father used to warn me not to "look like a plough jockey up from the country". Andrew, leaving the front of the station, possibly looking around, might have been seen in that way.