Is this water body at this pier a lake which is let's say fed by a river or an actual flowing river? I was told it's an actual lake. I'm very confused now. TIA.

Yes it is River and park is one of the many Riverside access you can enjoy on the Catawba River.

Lake wylie is a member of the Catawba River lake chain that originates in Black Mountain NC, creating a series of lakes ending in the harbor of Charleston SC. Loftin Park is a riverside park located on the Catawba River.

It's called a riverfront Park & it's supposed to provide access to the Catawba River. I think maybe when you're at the park, looking at that body of water, it looks a lot like a lake but that's not correct. It is a river. It has had calm waters & nice surroundings. Hopefully that answers your question.