In such cases as the picture in the link he red road marking has no legal force it is just used to highlight the area of the bus bay. Some councils do this in particular bus stops when there is a particular problem with illegal parking.
Consideration should be given to applying a contrasting surface colour within bus stop areas at selected stops where the level
of parking infringement within the bus bay has proved to be a particular problem.The most suitable and readily available colour is red.
Source Bus Stop design guide for Northern Ireland
! it is borrowing from the use of red routes colour scheme though.
The actual bus stop is designated by the dotted yellow lines and the road marking bus stop as illustrated in Highway Code Guide to Road Marking this puts in place parking restrictions in such bus stops.
On a single lane road where such bus stops and marking exist cars can pass through such a stop as long as they do not parking in it or obstruct a bus trying to use it.