Yup - unfortunately we have to get back to @QuietWyatt's original answer here - our infrastructure is not well suited to booleans, and you'll see bogons like this (averages that are not an integer, despite only integers being reported). A further catch on our infrastructure which is what lead to the 1.09 value - if your plugin reports a bit less than every 60 seconds, it might double-report for a period. A bit more, and there might be a "0" in there that does not correspond to a report (0 = no data, which could also happen during a network hiccup, or if your JSON data is malformed and thus not accepted).
Short answer is that for purposes of alerting, there's no good way to alert on a boolean value within a plugin. However in our app agents, we do much better at alerting on error rate and in our availability monitor (with an externally available URL), we do great substring checking with smart alerting that can withstand temporary network hiccups and is more configurable.
Sorry to say "you can't do that the way you're trying to", but at the moment, it's the truth. We'd be happy to lodge a feature request for you (which doesn't guarantee a fix, but which does mean that if we implement one, we'll let you know) in case neither of the above workarounds are sufficient - just let us know.