"Very high similarity" for a standard Bowtie2 output

I've created a SAM file from reads using Bowtie2 according to the standard Bowtie2 example.
When I tried to open the result file ("eg1.sam") in UGENE, the "Select correct document format" dialog appeared. It showed that BAM/SAM file import has score 8 (very high similarity).
Why is that? What's wrong with the file? Maybe the import should be corrected to include such standard cases.