I've noticed a few more strong similarities recently, I'd not listened to much Buxtehude but I now have a 6 CD set of his organ works, so getting more familiar.
Bach was influenced by loads of composers, from all countries. Copying, learning, incorporating it in his own composing style, et cetera. When organ composing is concerned, he most certainly was inspired by Reincken, Böhm, Buxtehude, Pachelbel, De Grigny, Couperin, Frescobaldi, Vivaldi plus all the others I forget to mention.
Also: we have to realize that most of the melodies of his organ works are not by himself. The chorale works (preludes, fantasias, partitas et al) are all based on original Lutheran hymns. And for a lot of free works he treated church & folk tunes together with inspiring tunes from other composers in the same way. This being quite common in those days .... but isn't it still?
(Post scriptum: one of Bach's most famous Fugues, the 2nd part of BWV 542 in G minor, was based on a Dutch folk song called
Ick ben gegroet [= I am saluted]. In Bach's time, this song was also well-known in the northern parts of Germany, like Hamburg. Hence the suggestion that it was composed for and played during Bach's application in Hamburg, where Dutch composer Johann Adam Reincken still had great influence.)