Firstly and most importantly: You are not a bad sub! I genuinely don't believe there is such a thing as a bad sub, he may have been a bad Dom, there are plenty of bad Doms... Thanks, I'm sure, in no small part to the popularity of 50 Shades of Grey a lot of people suddenly seem to think just being an asshole is a great way to get women! But if you're willing to submit your part in the dynamic is done, the Dom has the control [1] and it is his duty to find out what works for you both. Of course he not have been a bad Dom, maybe the two of you were just incompatible, think of vanilla relationships; just because you have a boy and a girl doesn't mean they are a match! Likewise just because he's a Dom and you're a sub that is far from a guarantee of compatibility.
Even if there was compatibility to start with I'd say him simply disappearing has ended it, the dynamic is based on trust. If you can't both trust each completely then it falls apart. Without trust a D/s relationship is dangerously close to simply being an abusive one, and if he can't handle his role in the dynamic then he can't be trusted. This is all on him, please don't feel any guilt yourself.
[1] Note: I say the Dom has control, but this isn't total, only within the constraints of the sub. She should have equal power setting limits, defining the relationship, agreeing dynamics, etc. There should be absolute trust established between them then he has control within them.
Now obviously from what you wrote I only get one side of the story, but I'll reassert you are not a bad sub and did nothing wrong. You certainly didn't deserve ghosting and that reflects badly on him, just walking away without explanation is weak. Sure sometimes alone time is needed, if he just needed a while to clear his head, or to deal with other stuff - but a few seconds to say sorry and keep you updated is not too much to ask [2]. And sometimes giving you alone time is a valid punishment leaving you to consider what you'd done, but since you were doing the task that doesn't seem to be the case, and even if it was it isn't something you leave open ended, you set the duration so they can count it down and explain why you're doing it.
[2] In past relationships I have done this twice, once a storm took out power and I went two days with no internet or means of charging my phone, being online I had no other means of communication. And the other time I was in hospital. But on both occasions getting back in touch to apologise was a priority as soon as it was possible... And since he managed to say he had been busy he clearly could make contact, but doing so without apology and without explanation or estimate of when he'd be back just makes him a dick!
TL;DR - You're not a bad sub, you took on your role and did your task as instructed nobody could ask more of you. Most likely he's a bad Dom, and certainly the two of you simply weren't compatible. If you want to ask any more questions feel free to inbox.