You are saving the PDF with crop marks and bleeds included, which is optional and only useful when sending a PDF to a print shop.
If that's your intention, then the PDF is fine, and you should not be concerned with the issue. This is how InDesign will save a single page PDF with crop marks and bleeds, and the print shop has probably seen this before. Excess artwork flows into the facing page's bleed area, but all this is supposed to be removed during production.
Another solution here is to change the document from FACING PAGES to SINGLE PAGES in the
Main Menu → File → Document Setup panel. Be advised doing this can potentially have other effects on your pages, so only use this if you have full control of your document.
However, if you need to remove these crop marks and bleeds, when you save the PDF, in the Export dialog box, unselect all the boxes marked in red below. Make sure they are not selected, and try again.