There is no (direct) connection between the verbs anschnallen and anschneiden but there could be an explanation for why you mistook the one for the other:
In some German dialects there are positions where an L-sound gets vocalized. For example, the Bavarian pronunciation of
anschnallen is something like [o:schnåin]
where å denotes a dark a sound and the Bavarian pronunciation of
anschneiden is something like [o:schnain].
(For this custom-made phonemic transcription see for example this Bavarian dictionary.)
So in Bavarian the words anschnallen and anschneiden are pronounced very similarly but the ai diphthongs are different. There may be other regions/dialects where both words have a similar pronunciation.
Possibly your friend is a speaker of one of these dialects that have an L-vocalization, so that in his/her speech both words are similar.