As it's a Bf109E, it's very possible that those presumed 'ground' kills were in the early part of the war, that is, from September 1939 to maybe May or June 1940. This would certainly have allowed opportunities to destroy, or claim destroyed, Polish, French, Belgian, Dutch and RAF aircraft on the ground. At a guess, I'd say the victory markings were an unofficial, personal tally.
I think I might have some more info somewhere, and possibly some clearer pics showing dates and national markings on the abschuss zeichen, not necessarily of this aircraft, which might add something - if I can find which book(s) they're in.