i think there are a lot of the same characteristics in BPD and autism. for example:
-black and white thinking
-meltdowns and shutting down over “small” stimuli
-feeling more intensely than neurotypical people 
-problems understanding others in social situations 
-emotions often felt in body rather than mind (this might just be a personal thing)
 struggling to think of more but I’ll add in the comments if I can think of any more. I have read every research paper I could find about the concurrence of the two conditions but there’s not a lot unfortunately. let me know if anyone else has thoughts about this!