Spotlight is disabled for my main volume
I noticed a similar error once in console.  If I recall, very similar errors start occurring regularly above 80% capacity, meaning you haven't freed up nearly enough yet.

There are several system activities that potentially eat a significant amount of space, like creating a new swap file. To protect such activities, Apple deactivates some space consuming activities, including indexing, once the drive is 80% full. 

There might be system tuning parameters which you could tweak that control this.  In fact, those errors get seen vastly more often than mdutil's errors, meaning you might learn more by opening console, identify the related errors, and google them.

I've learned to consider all those annoying log messages a "feature" myself though since leaving 50ish gigs free for temporary emergency usage has more "utility" than filling that space with infrequently used junk.