Your Ex seems to have had several issues, and they May not have all been related to a mental disorder/ illness. Here is what I see:

1- Peeing in bottles can be caused by laziness, anti social (avoiding bathroom Journey not to run into other people), secrecy (avoiding shared family toilet not to Let family know you are still awake at 3am), convenience, habit, fetish, OCD (like the Aviator), mischieviousness/fun, instant relief, monitoring color/volume, depression … any one or any combination of the above. So it May have been impossible for you to find the right answer. And it’s possible your ex was being truthful When he said “I dont know”. It is slso possible that he knew the answer but was not willing to share it (for whatever reason)

2- BUT I think that to leave the bottles around the house is another issue. I think its behavioral. It’s one thing to relieve oneself in a bottle & completely different thing to leave it in the open for all (your wife) to see.  I think this detail is about a lack of manners / self awareness / etiquette/ it’s just rude. Its the equivalent of farting / burping in front of people. Many people feel uncomfortable/embarassed to release gas or farting sounds in front of others. For those people, it is rude/ unbecoming / uncivilized etc. Apparently, your EX didn’t have this instilled in him. The question I would ask is this: did he leave piss bottles at his work ? I doubt it. And The reason he probably didn’t is he had the self awareness & restraint & good sense not to. He was able to compartmentalize & act appropriately. He probably used the WC at work. Or if he really had a compulsion to piss in bottles, He may have secretly pissed in them at work … but he definitely would have ensured no one saw the bottles. He would have concealed & emptied them promptly. Because he knew it wouldn’t reflect well on him. 

3- Elaborating on why he let you find the bottles… I’d say it’s possible he had no inhibitions around his partners/wife. Maybe that inhibition totally dropped at home. Again, this is also related to behavior / rudeness. To put it bluntly, it sounds like your EX had no class. He may have concealed it during the courtship/ honeymoon phase. 

4- His high school sweetheart probably knew this about him since their student days. Probably laughed about it when they were kids. And it probably became a habit of his since those days. 

Any of the above could be true. And no where do I see that it could have been your fault. It was unrelated to you. It couldn’t have been averted. I don’t even think that he was deliberately trying to annoy or send you a message or mistreat you with this action. Nor was this “a call for help”. This was something very personal within himself & it spilled over into your space (he scattered the bottles) because he had other issues like lack of inhibition/ self awareness/ self restraint / class.