Based on the question you were asked I’d say they meant 5pm.
We literally have this thread on Mumsnet twice a week! 
Tea for northerners and working class people is generally the evening meal, eaten between 5-7pm.
Tea for middle class or southern people generally means cake and sandwiches between 3-5pm.
Northerners and working class people often call lunch “dinner”.
Dinner to middle class and southern people is the evening meal, eaten around 7pm ish.
The class thing comes from meals being eaten at different times to fit old working patterns. The leisured classes didn’t really work so they ate breakfast, lunch, tea and dinner and took time over it, eating later.
Working class people ate (if they were lucky) breakfast, dinner and tea earlier to fit with changeovers in shifts or eating earlier than the family if they were in service. That’s the legacy behind it all.
In our house we eat our evening meal (dinner) early at 5.15pm or so, so we can eat with DS. It’ll move later as he gets older.