Resume own naviation on course

I'm VFR at 2,500 ft AGL with a course that will in 10 minutes take me
through a Class D airspace. I contact flight following, ATC gives me a
squawk code and says, "Resume own navigation on course. Do not enter
class D airspace."

Huh? If I continue on course, I will go through the Class D airspace.
What did they mean by "Resume on navigation *on course.* Do not enter
Class D airspace."

I asked for clarification twice, but merely got the same sentence
repeated each time.

So I changed course and avoided the Class D airspace. I suppose I could
have gained some altitude and gone over the top.

But I still don't know why *on course* was in the instruction. Any
ideas?

John Hudson Tiner