I may be mistaken, but I don't believe Glock will sell those to private citizens.
Doesn't make it impossible, just extraordinarily unlikely.
Glock doesn't sell G18s to non-LEO/Mil in the US. There are a few (less than 10?) pre-86 dealer samples in private hands. So, I don't think that it was an 18, unless there is a very rich gun collector (with a Class 2 FFL) out there waiting to lose it...
You're right the Glock 18 is a LEO and Military only gun, that's why I said it was highly doubtful.