No that shouldn't be serious. Some large file was removed, but was still in use when the drive was remounted readonly. So it was only 'marked' for deletion (deleted inode has 0 dtime), but never really reclaimed. When that is 'fixed' the blocks that were part of this file are no longer referenced, but the allocation bitmap still shows them as used. those are the block bitmap differences. Finally the free blocks counts are corrected, as long as the number of free blocks increases it should be safe.

It actually looks like 2 files were deleted, as the inode count was off by 2. Both of them were about 228 blocks, so about 228KB or 872KB depending on the filesystem blocksize.