Red is probably the most popular color for the very idea of colors, since it’s not as common in nature, it’s one of those things that we instantly notice when we see it, plus, it’s the color of apples, so if you grew up learning English, it’s literally in the front of your mind as the color attributed to probably the thing most often used for analogical examples in early life.

Hammers likewise are the tool by excellence for most people. Their usage is crystal clear by only holding one, anyone can use one, and their design is so standard that it’s pretty much impossible to match how iconic they can be, I’d argue they’re only matched by the saw in terms of how many people have them as their top most iconic tool.

Lastly, the way it was worded made you think of both things separately, making it almost certain that you’d pick the top items for each category. I’m pretty confident that if anon had asked for a “tool and also what color is it?” instead of a color AND a tool, you’d most likely would’ve gone with a yellow hammer, since yellow is typically associated with construction, same as tools.