I should imagine by now you've gotten your answer, but in future check with your landlord if anyone wants to come in and you aren't sure they're supposed to be there.
But for the sake of others moving over, and EPC rating is for the energy efficiency of the entire house/flat. They check the Windows, insulation, boiler, radiators, if there's a thermostat, what the house is made of, even whatlightbulbs are used. They then make a report based on all the info they've gathered, and give the property an energy rating along with suggestions for improvements, if needed.
I wish we had it here in the US. The first house we rented was super cheap in a really nice area. We found out why after moving in: $400/mo heating cooling bills! 😮