Due to privacy laws, WWE won't offer any explanation around Hornswoggle's 30 day suspension for violating the Wellness Policy. However, PWInsider are reporting that if WWE learns of an arrest that would violate company policy, that would be one reason they would have tested Hornswoggle at his home. Another explanation could be that his name just came up for random testing, and as he wasn't on the road, they attended his home and caught him out. Another explanation is that Hornswoggle couldn't physically provide the test. A rumour going around is that he was surprised by the testers, and wasn't able to provide urine in the three hour window of them turning up. You'd think maybe he could have just consumed a load of water, but the rumour states he just wasn't able to provide a sample in the testing window. As a result, he was considered a fail. There's no way of knowing for sure what has gone down, but it isn't like the failure is too serious. Several WWE talent have served the 30 day suspension and then came back to the main roster. Test failures are less common now, but going back a few years there were several wrestlers caught out. Hornswoggle was inactive and there were no plans on the horizon for his character, his suspension will come and go without much fuss.
