True - but not totally reliable.
Sheffield is often quoted as the greenest city in Europe - but that is also a bit misleading. One third of Sheffield is in the Peak District National Park, and there are loads of parks (if not as many trees as a few years ago!) - many of them big. But there are still large swathes of the city that are covered by big estates, similar to most major cities in the UK, that are mostly brick, tarmac and concrete.
Number of parks and acreage are useful indicators - but spread of green space and access are also important.