from the report, the crew believe they where waiting for them. The bombers where level at 20,000 ft, a bit high for the Ju 87. However, the ceiling service for the Ju 87 is 26,000 ft. I am sure they could not get above 20,000 ft but there could have been that chance that they did. as soon as they saw them coming, It would be a one pass at them and i am sure it would have been a HO pass to.
The only way a Ju87 would engage a B17 would be a random account with a wounded straggler at low alt.
there was nothing in the report of that.