I wouldn't read too much in to it.
In fact I think it is a good move by Wizz and it gives them coverage further south of London.
They have already moved in to BHX and I guess they will look to offer more destinations at LGW if slots are available at the right times.
It's not as if they are consolidating at LTN because they are still launching new flights.
Couple that with what Powerjet1 has said I think it makes sense.