Find-A-Grave isn't necessarily correct - it's a crowdsourced site.
If Biden were buried in Arlington Cemetery, he'd be here and he's not: https://www.arlingtoncemetery.mil/Explore/Notable-Graves/Presidents
Also, the FindAGrave memorial has been removed, although it still appears in the index search as seen above:
INDEX: https://www.ancestry.com/discoveryui-content/view/238124728:60525?tid=&pid=&queryId=22dbb4ce-9367-4ce5-ada5-1c3eada31f46&_phsrc=vDw1&_phstart=successSource
REMOVED: https://www.findagrave.com/memorial/267327344/joseph-robinette-biden?_gl=1y73dgg_gcl_auNDcyOTM1NzIuMTcxMjE3NTE5NQ.._gaODkzMjIxODg0LjE3MTIxNzUxOTY._ga_4QT8FMEX30ZjUyZGY2MGQtMWVhNS00YmVkLTllZjEtYjEzNmI4Y2YwNTQyLjMzLjAuMTcxODIxNjUxMy42MC4wLjA._ga_LMK6K2LSJH*ZjUyZGY2MGQtMWVhNS00YmVkLTllZjEtYjEzNmI4Y2YwNTQyLjMzLjAuMTcxODIxNjUxMy4wLjAuMA..