Essentially his players weren’t sure how the speed mechanic mapped itself to the traditional Dexterity/Agility/Move statistics used in most RPGs.
That's understandable since its name alone does little to explain that mapping well and the one-page format doesn't leave space for a full discourse on the breadth of a given Attribute's scope.
A cursory review may lead to an opinion that Speed only deals with how fast one can move successfully. And while that's correct, it is also just the tip of the iceberg. The issue lies in that fact that players may stop at that definition, unwilling to think how that definition actually explains things deeper.
To further complicate the matter, squarely at the root of the question is the fact that Attributes in the d6-lite framework are handled as typical RPG feats and skills, a fact which subsequently leads to questions of what a Feat of Speed encompasses.
The seeds of a full answer lie in that short description: "how fast one can move successfully." But for some, making the quantum leap to "can one X successfully?" might need some nudging.
A Caveat:Always remember that the framework is consciously designed to be so simplistic that many parts of the whole can, and should, be interpreted in many ways. That's not a failing of the system; rather it is one of the d6-lite framework's greatest strengths. Feel free to make a ruling that makes the most sense to you and your players, even one that might directly oppose my viewpoint.
That said, here's how I answered his question:
Speed:Both. Speed is the ability to perform manual tasks quickly and successfully since "quick" is just a time-based measure of skill.
One of the interesting things about the d6-lite framework is in how Feats of X are handled. Feats are only tested when the task is opposed in some fashion (the opposition may be active like that of an opponent, or passive like that of an inanimate object like a lock.) So typically, if a character isn't being pressured by a time constraint, then it's assumed whatever task they are attempting would succeed given enough time and effort.
However, that's not always the case.
Since Feats are always considered opposed tasks, in some cases success is assumed but the test is in quickness while in others success based on ability is what's being tested. For example, a Feat of Strength can fail and indicate that no matter how long a character tries to force open a box, they will fail.
Likewise Speed is used when a character has all day but the task can't be resolved in a reasonable period of time as well as when the task requires precision. Failure indicates that no matter the time constraint, the character cannot perform the task.
From a simple viewpoint both are really tests of time. On one scale the character must do something before a time constraint runs out, while the other is a failure of not doing something given the time constraint.
So...
- Running from something would be a Feat of Speed. Failure would indicate being caught.
- Finding the right key in the dark while something terrible is coming down the hall is a Feat of Speed. Failure would indicate the key is either not found or didn't successfully get used to unlock whatever.
Just as...
- Crossing a slippery plank would be a Feat of Speed regardless of the time given.
In this case the failure of a feat of speed indicates failure of the task in the time allotted just as the prior 2 examples. Hope that actually clears things up and doesn't confuse it more.
Of course you can just as easily ignore all the above and make a ruling logical to your play style and I won't be the slightest bit offended.