Random nether portal.

So I loaded my world up and as soon as I left my house I saw a nether portal hovering over the ocean built and lit but my portal was still working on both sides but when I left the nether it put me at the one over the ocean. Overworld coordinates for my portal are 4670, 79, -1369. Nether coordinates 571, 100, -155

 Random ocean portal is at 4555, 99, -1227. I already explored before hand and did not see this.